Transcript Vector Calculus

Limit and Continuity
2.1 Rate of Change and Limits (1)
Average and Instantaneous Speed
Example 1 FINDING AN AVERAGE SPEED
A rock falls from the top of a tall cliff. What is the average
speed during the first two seconds of fall ?
Solution
The displacement will be y (t )  16t 2
according to the definition
y
y 16(2)  16(0)
average speed 

t
2
 32 ft/sec
2
2
y
2.1 Rate of Change and Limits (2, Example 2)
Average and Instantaneous Speed
Example 2 FINDING AN INSTANTANEOUS S PEED
A rock falls from the top of a tall cliff. What is the
instantaneous speed during at t  2 sec. of fall ?
Solution
Using the definition of average speed with t  2 and
t  2  h (where h =small)
y 16(2  h )2  16(2)2
AV 

 64  16h ft/sec
t
h
h
When different
value of h
AV
1
80
0.1
0.001
0.00001
65.6
64.016
64.00016
y (t )  16t 2
y
t=2
v=?
2.1 Rate of Change and Limits (3)
Definition of Limit
Definition Limit
Let c and L be real numbers. The function f has limit L as x
approaches c if, given any postive number , there is a
postive number  such that for all x ,
0  x - c    f (x )  L  .
lim f (x )  L
We write
x c
y
The sentence lim f (x )  L is read
L

x c

"The limit of f of x as x approaches

c equals L"

c
x
2.1 Rate of Change and Limits (4)
Definition of Limit
-2
(c) h (x )  x  1
3
3
3
2
2
2
1
1
1
0
0
0
-1
0
1
-1
2
x 2 1
(a) f (x ) 
x 1
-2
-1
0
1
2
-2
x 2 1
, x 1

(b) g (x )   x  1
 1,
x 1
-1
limf (x )  lim g (x )  limh (x )  2
x 1
x 1
x 1
-1
0
-1
1
2
2.1 Rate of Change and Limits (5)
Properties of Limit
Two Basic Function Limits
lim k  k
a constant function f (x )  k
lim x  c
an identity function f (x )  x
x c
x c
This can be applied to do the limits of all polynominal
and rational functions.
2.1 Rate of Change and Limits (6, Theorem 1)
Properties of Limit
Theorem 1 Properties of Limit s
If L, M , c , and k are real numbers and
lim f (x )  L and lim g ( x )  M , then
x c
1. Sum Rule :
x c
lim(f ( x )  g ( x ))  L  M
x c
The limit of the sum of two functions is the sum of their limits.
2. Difference Rule :
lim(f ( x )  g ( x ))  L  M
x c
The limit of the difference of two functions is the difference of
their limits.
3. Product Rule :
lim(f ( x )  g ( x ))  L  M
x 
The limit of a product of two functions is the product of their limits.
2.1 Rate of Change and Limits (7, Theorem 1)
Properties of Limit
Theorem 1 Properties of Limit s
If L, M , c , and k are real numbers and
lim f ( x )  L
x c
and
lim g ( x )  M , then
x c
4. Constant Multiple Rule :
lim(k  f ( x ))  k  L
x 
The limit of a constant times a function is the constant times the
limit of the function.
5. Quotient Rule :
f (x ) L
lim
 , M 0
x  g ( x )
M
The limit of a quotient of two functions is the quotient of their
limits, provided the limit of the denominator is not zero.
2.1 Rate of Change and Limits (8, Theorem 1)
Properties of Limit
Theorem 1 Properties of Limits
If L, M , c , and k are real numbers and
lim f (x )  L
x c
and
lim g (x )  M , then
x c
6. Power Rule : If r and s are integers, s  0,then
lim(f (x ))r
x c
provided that Lr
s
s
 Lr
s
is a real number.
The limit of a rational power of a function is that power
of the limit of the function, provided the latter is a real
number.
2.1 Rate of Change and Limits (9, Example 3)
Properties of Limit
Example 3 USING PROPERTIES OF LIMITS
Find the limit of (a) lim  x 3  4x 2  3  , (b)
x c
x

lim
x c
Solution
(a) lim  x 3  4x 2  3   lim x 3  lim 4x 2  lim 3
x c
x c
x c
 c 3  4c 2  3
(b)
x

lim
x c

4
 x  1
lim  x 4  x 2  1
2
x2 5
x c

lim  x 2  5 
x c
lim x 4  lim x 2  lim1
x c
x c
x c
lim x  lim 5
2
x c
x c

4
2
c

c
 1

c2 5
x c
4
 x 2  1
x2 5
2.1 Rate of Change and Limits (10,Theorem 2)
Properties of Limit
Theorem 2 Polynomial and Rational Functions
1. If f (x )  an x n  an 1x n 1 
 a 0 is any polynomial
function and c is any real number. then
lim f (x )  f (c )  anc n  an 1c n 1 
x c
 a0
2. If f (x ) and g (x ) are polynomials and c is any real
number, then
f (x ) f (c )
,

x c g ( x )
g (c )
lim
provided that g (c )  0
2.1 Rate of Change and Limits (11, Example 4)
Properties of Limit
Example 4 USING THEOREM 2
Find the limit of (a) lim  x (2  x ) , (b)
2
x 3
x

lim
x 2
Solution
(a) lim  x 2 (2  x )  32 (2  3)  9
x 3
(b) lim
x 2
2
x
  2x  4 
x 2

2
2
  2(2)  4 
22
3
2
 2x  4 
x 2
2.1 Rate of Change and Limits (12, Example 5)
Properties of Limit
Example 5 USING THE PRODUCT RULE
tan x
Find the limit of (a) lim
x 0
x
Solution
lim
x 0
tan x
x
 lim
x 0
 lim
x 0
sin x
x
sin x
x
1
cos x
1
 lim
x 0 cos x
1
 1
1
cos 0
2-1 Exercise 63
2
0
-4
-2
-2
0
2
4
2.1 Rate of Change and Limits (13, Example 6)
Properties of Limit
Example 6 EXPLORING A NONEXISTENT LIMIT
Find the limit of
x 3 1
lim
x 2 x  2
Solution
From graph,
200
it does not exist.
100
0
-100
-10
-5
0
5
10
2.1 Rate of Change and Limits (14)
One-sided and Two-sided Limits
Definition
right-hand
left-hand
lim f ( x ) The limit of f as x approaches c
x c
from the right.
lim f ( x ) The limit of f as x approaches c
x c
from the left.
f(x)
f(c-) f(c+)
c
x
2.1 Rate of Change and Limits (15, Example 7)
One-sided and Two-sided Limits
Example 7 FUNCTION VALUES APPROACH TWO NUMBERS
Find the limit of f ( x )  int( x )
Solution
lim int( x )  0
5
lim int( x )  1
3
x 1
x 1
4
2
1
0
-1
-2
-3
-2
-1
0
1
2
3
4
5
2.1 Rate of Change and Limits (16, Theorem 3)
One-sided and Two-sided Limits
Theorem 3 One - sided and Two - sided Limi ts
A function f ( x ) has a limit as x approaches c if and only if the
right-hand and left-hand limits at c exist and are equal.
In symbols,
lim f (x )  L  lim f (x )  L
x c
x c
and
lim f ( x )  L
x c
2.1 Rate of Change and Limits (17, Example 8)
One-sided and Two-sided Limits
Example 8 EXPLORING RIGHT- AND LEFT-HAND LIMITS
Find the limit of
 x  1, 0  x  1
 1,
1 x  2
lim f (x )  0


x 1
x 2
 x  1, 2  x  3

x  5, 3  x  4
f (x )  
3
2,
lim f (x )  1
x 1
lim f ( x )  1
x 2
lim f ( x )  1
x 2
2
lim f ( x )  2
x 2
lim f ( x )  2
1
x 3
x 4
x 3
x 4
lim f ( x )  2
0
0
1
2
3
4
5
lim f (x )  1
lim f ( x )  2
x 3
lim f (x )  1
2.1 Rate of Change and Limits (18, Theorem 4)
Sandwich Theorem
Theorem 4 The Sandwich Theore m
If g (x )  f (x )  h (x ) for all x  c in some interval about c ,
and lim g (x )  lim h (x )  L, then lim f ( x )  L
x c
x c
x c
y
h
L
f
g
c
x
2.1 Rate of Change and Limits (19, Example 9)
Sandwich Theorem
Example 9 USING THE SANDWICH THEOREM
Show that lim x 2 sin(1/ x )  0
x 0
Solution
since
and
Finally,
 x 2  x 2 sin  1x   x 2
lim( x 2 )  lim( x 2 )  0
x 0
x 0
lim x 2 sin  1x   0
x 0
0.02
h(x) = x2
0.01
0
-0.01
f(x) = x2 sin(1/x)
g(x) = -x2
-0.02
-0.2
-0.1
0
0.1
0.2
2.2 Limits Involving Infinite (1)
Finite Limits as x→±
• The symbol of infinite () does not represent a real
number.
• The use  to describe the behavior of a function when
the values in its domain or range out grow all finite
bounds.
The limit of f as x approaches infinite means
the limit of f as x moves increasingly far to the right on
the number line (x  ).
the limit of f as x moves increasingly far to the left on
the number line (x  ).
The limit in each case may or may not exist.
2.2 Limits Involving Infinite (2)
Finite Limits as x→±
Looking at
-6
f (x )  1/ x
-4
-2
0
2
4
6
(a) as x  , (1/ x )  0 and we write lim(1/ x )  0
x 
(b) as x  , (1/ x )  0 and we write lim (1/ x )  0
x 
2.2 Limits Involving Infinite (3)
Finite Limits as x→±
Definition Horizontal Asymptote
The line y  b is a horizontal asymptote of the graph
of a function y  f (x ) if either
lim f (x )  b
x 
Looking at
or
lim f (x )  b .
x 
f ( x )  2  1/ x
1
1


lim  2    2 and lim  2    2
x  
x  
x
x
This function has the single horizontal asymptote
y 2
2.2 Limits Involving Infinite (4, Example 1)
Finite Limits as x→±
Example 1 LOOKING FOR HORIZONTAL ASYMPTOTES
x
Investigate the graph of f ( x ) 
x 2 1
Solution
From graph shows
 x

lim 
 1 and

2
x 
 x 1
 x

lim 
  1
2
x 
 x 1
This function has the two horizontal
asymptotes
y  1 and y  1
1
0
-8
-4
0
-1
4
8
2.2 Limits Involving Infinite (5, Example 2)
Sandwich Theorem Revisited
Example 2 FINDING A LIMIT AS x APPROACHES 
sin x
Find lim 
x 
x
Solution
since,
-1  sinx  1, for x  0
-1 sin x 1


x
x
x
by Sandwich theorem
1
sin x
1
 -1 
0  lim    lim
 lim
x   x 
x 
x  x
x
0
-10
0
-1
10
2.2 Limits Involving Infinite (6, Theorem 5-1)
Sandwich Theorem Revisited
Theorem 5 Properties of Limits as x → ±∞
If L,M, and k are real numbers and
lim f (x )  L
and
lim g (x )  M ,then
x 
1. Sum Rule :
2. Difference Rule :
3. Product Rule :
4. Constant Multiple Rule :
x 
lim (f ( x )  g (x ))  L  M
x 
lim (f ( x )  g ( x ))  L  M
x 
lim (f ( x )  g ( x ))  L  M
x 
lim (k  f (x ))  k  L
x 
2.2 Limits Involving Infinite (7, Theorem 5-2)
Sandwich Theorem Revisited
Theorem 5 Properties of Limits as x → ±∞
If L, M , and k are real numbers and
lim f ( x )  L
and
lim g ( x )  M , then
x 
x 
f (x ) L
5. Quotient Rule :
lim
 ,M  0
x  g ( x )
M
6. Power Rule : If r and s are integers, s  0, then
lim (f (x ))r
s
x 
provided that Lr s is a real number.
 Lr
s
2.2 Limits Involving Infinite (8, Example 3)
Sandwich Theorem Revisited
Example 3 USING THEOREM 5
5x  sin x
Find lim 
x 
x
Solution
5x  sin x
5x sin x
sin x
since,


5
So,
x
x
x
x
5x  sin x
sin x
lim
 lim 5  lim
5
x 
x 
x 
x
x
6
4
2
-10
0
-2
-4
-6
0
10
2.2 Limits Involving Infinite (9, Exploration 1-1)
Sandwich Theorem Revisited
Exploration 1 Exploring Theorem 5
1. Let f (x )  5x  sin x , g (x )  x . Can we apply Quotient
Rule to lim f ( x ) / g ( x )? Does the limit exist ?
x 
6
5
4
-60 -40 -20
0
20
40
60
2.2 Limits Involving Infinite (10, Exploration 1-2)
Sandwich Theorem Revisited
Exploration 1 Exploring Theorem 5
2. Let f (x )  sin2 x , g (x )  cos 2 x . Describe the
behavior of f and g as x   ? Can we apply the
Sum Rule to lim(f (x )  g (x ))  ?
x 
2
f(x) = sin2x
g(x) = cos2x
1
0
0
5
10
15
20
25
2.2 Limits Involving Infinite (11, Exploration 1-3)
Sandwich Theorem Revisited
Exploration 1 Exploring Theorem 5
3. Let f (x )  ln(2x ), g ( x )  ln( x  1). Find the limit of f and
g as x   ? Can we apply the Difference Rule to
lim(f (x )  g (x ))  ? Does the limit exist
x 
4
3
2
1
f(x) = ln(2x)
g(x) = ln(x+1)
0
-1
0
5
10
15
20
25
2.2 Limits Involving Infinite (12)
Infinite Limits as x →a
Looking at
(a) as x  0  ,
(b) as x  0  ,
f ( x )  1/ x
lim (1/ x )  
x 0
lim (1/ x )  
x 0
-6
-4
-2
0
2
4
6
2.2 Limits Involving Infinite (13)
Infinite Limits as x →a
Definition Vertical Asymptote
The line x  a is a vertical asymptote of the graph
of a function y  f (x ) if either
lim f (x )  
or lim f (x )  .
x a
x a
2.2 Limits Involving Infinite (14, Example 4)
Infinite Limits as x →a
Example 4 FINDING VERTICAL ASYMPTOTES
Find the vertical asymptotes f ( x ) 
Solution
since, lim
x 0
1
x
2
  and lim
x 0
1
x
2
1
x2

line x  0 is the only vertical asymptote.
4
3
2
1
0
-12
-8
-4
0
4
8
12
2.2 Limits Involving Infinite (15, Example 5)
Infinite Limits as x →a
Example 5 DINDING VERTICAL ASYMPT OTES
Find the vertical asymptotes f ( x )  tan x
Solution

when a  n , (n  odd integer),
2
lim tan(x )   and lim tan x  
x a
x a
4
2
0
-8
-4
-2
-4
0
4
8
2.2 Limits Involving Infinite (16, Example 6)
End Behavior Models
Example 6 MODELING FUNCTIONS FOR | x | LA RGE
Let f (x )  3x 4  2x 3  3x 2  5x  6 and g ( x )  3x 4
Solution
The graph f and g , quite different near the origin,
are identical on a larger scale.
f (x ) 3x 4  2x 3  3x 2  5x  6
lim

1
4
x  g ( x )
3x
20
40000
15
10
20000
5
0
0
-5
-2
-1
0
1
2
-20
-10
0
10
20
2.2 Limits Involving Infinite (17)
End Behavior Models
Definition End Behavior Model
The function g is
(a) a right end behavior model for f if and only if
f (x )
lim
1
x  g ( x )
(b) a left end behavior model for f if and only if
f (x )
lim
1
x  g ( x )
2.2 Limits Involving Infinite (18, Example 7)
End Behavior Models
Example 7 FINDING END BEHAVIOR MODELS
Let f ( x )  x  e  x , show that g ( x )  x is a right end behavior
model for f while h ( x )  e  x is a left end behavior models for f .
Solution
on the right
 e x
f (x )
x  e x
lim
 lim
 lim  1 
x  g ( x )
x 
x 
x
x


 1

on the left
f (x )
x  e x
x

lim
 lim
 lim  1   x

x
x  h ( x )
x 
x  
e
e
8

 1

4
0
-8
-4
0
4
8
2.2 Limits Involving Infinite (19)
End Behavior Models
• IF one function provides both a left and right behavior
model, it called an end behavior model.
• In general, g(x) = anxn ia an end behavior model for
the polynominal function f(x) = anxn + an-1xn-1 +…+ ao .
In the large, all polynominals behave like monomials.
• This is the key to the end behavior of rational
functions.
2.2 Limits Involving Infinite (20, Example 8)
End Behavior Models
Example 8 FINDING END BEHAVIOR MODELS
Find the end behavior model for
2x 3  x 2  x  1
2x 5  x 4  x 2  1
, (b) f ( x ) 
(a) f (x ) 
2
5x 3  x 2  x  5
3x  5x  7
Solution
(a) end behavior of numerator is 2x 5 , demominator
is 3x 2 , the end behavior model of f is
2
3
x3
(b) end behavior of numerator is 2x 3 , demominator
is 5x 3 , the end behavior model of f is
2
5
2.2 Limits Involving Infinite (21, Example 9)
End Behavior Models
Example 9 FINDING A HORIZONTAL ASYMPTOTE
4x 2  3x  5
Dose the graph f ( x ) 
have a horizontal
3
2x  x  1
symptote ? If so, what is it ?
Solution
The end behavior for f is 4x 2 / 2x 3  2 / x
so, lim f (x )  lim 2 / x  0,
x 
x 
y  0 is the horizontal asymptote of f .
8
4
0
-8
-4
0
4
8
2.2 Limits Involving Infinite (22, Example 10)
Seeing Limits as x→±
Example 10 USING SUBSTITUTION
lim sin(1/ x )
Find
x 
Solution
replacing lim sin(1/ x ) by the equivalent lim sin(x )  0
x 
then, lim sin(1/ x )  lim sin( x )  0
x 
-8
-4
x 0
x 0
2
2
1
1
0
0
-1
-1
-2
-2
0
4
8
-0.08
-0.04
0
0.04
0.08
2.3 Continuity (1, Example 1-1)
Continuity at a Point
Example 1 INVESTIGATING CONTINUIT Y
  x  1,
 1,

f ( x )   2,
 x  1,
 x  5,

3
0  x 1
1 x  2
x 2
2x 3
3x 4
Solution
2
This function f is continuous
at every point in its domain
1
[0, 4], except at x  1 and
x  2.
0
0
1
2
3
4
5
2.3 Continuity (2, Example 1-2)
Continuity at a Point
Example 1 INVESTIGATING CONTINUITY
Solution
point at which f is continuous
x  0,
lim f (x )  f (0)
x 0
x  4,
lim f (x )  f (4)
x 4
x  c , c  1, 2, lim f (x )  f (c )
3
point at which f is discontinuous
2
x c
x  1,
x  2,
lim f ( x )  does not exist
x 1
lim f ( x )  1, but 1  f (2)
1
x 2
0
0
1
2
3
4
5
2.3 Continuity (3)
Continuity at a Point
Definition Continuity at a Point
Interior Point : A function y  f (x ) is continuous at an interior point c
of its domain if
lim f (x )  f (c )
x c
Endpoint : A function y  f (x ) is continuous at a left endpoint a or is
continuous at a right endpoint b of its domain if
lim f (x )  f (a ) or lim f (x )  f (b ), respectively.
x a 
x b 
Continuity
from both side
Continuity
from the left
Continuity
from the right
a
c
b
2.3 Continuity (4, Example 2)
Continuity at a Point
Example 2 FINDING POINT OF CONTINUITY & DISCONTINUITY
Consider the integer function f ( x )  int( x )
Solution
For the function to be continuous at x  c ,
the limit as x  c must exist 5
4
and must equal the value of
3
2
the function at x  c .
This function is discontinuous
at every integer.
lim (int x )  2,
x 3
lim (int x )  3
x 3 
1
0
-1
-2
-3
the limit as x  n does not exist
-2
-1
0
1
2
3
4
5
2.3 Continuity (5)
Continuity at a Point
1
y = f(x)
y = f(x)
1
continuous at x=0
1
2
y = f(x)
continuous at x=0
If it had f(0)=1
continuous at x=0
If it had f(0)=1
continuity at x = 0 are
removable
2.3 Continuity (6)
Continuity at a Point
lim f (x ) does not exist, no way to
x 0
1
improve it. It is a trype of a jump
discontinuity.
y = f(x)
6
lim1/ x 2  ,
4
x 0
an infinite discontinuity.
2
0
-4
-2
0
2
4
2.3 Continuity (7)
Continuity at a Point
1
lim sin(1/ x ),
x 0
0
-1
an oscillating discontinuity.
2.3 Continuity (8, Exploration1-1,2)
Continuity at a Point
Exploration 1 Removing a Discontinuity
x 3  7x  6
Consider the function f (x ) 
x2 9
1. Factor the denominator. What is the domain of f (x )
2. Investigate the graph of f around x  3 to see that f
has a removable discontinuity at x  3
40
0
-4
-2
0
-40
2
4
2.3 Continuity (9, Exploration1-3)
Continuity at a Point
Exploration 1 Removing a Discontinuity
x 3  7x  6
Consider the function f (x ) 
x2 9
3. How should f be defined at x  3 to remove the
discontinuity ?
2.00
2.4000
2.90
3.2390
2.95
3.2861
2.99
3.3239
3.01
3.3428
3.05
3.3806
3.10
3.4279
4.00
4.2857
40
0
-4
-2
0
-40
2
4
2.3 Continuity (10, Exploration1-4)
Continuity at a Point
Exploration 1 Removing a Discontinuity
Consider the function
x 3  7x  6
f (x ) 
x2 9
4. Show that (x - 3) is a factor of the numerator of f ,
and remove all commond factors. Now computer
the limit as x  3 of the reduced form f .
40
0
-4
-2
0
-40
2
4
2.3 Continuity (11, Exploration1-5)
Continuity at a Point
Exploration 1 Removing a Discontinuity
Consider the function
x 3  7x  6
f (x ) 
x2 9
5. Show that the extended function
 x 3  7x  6
,
x 3

g (x )   x 2  9
10 / 3,
x 3

is continuous at x  3. The function g ( x ) is the
continuous extension of the original function f to
include x  3.
2.3 Continuity (12)
Continuous Functions
• A function is continuous on an interval if and only if
it is continuous at every point of the interval.
• A continuous function is one that is continuous at
every point of its domain.
2.3 Continuity (12, Example 3)
Continuous Functions
Example 3 IDENTIFYING CONTINUOUS FUNCTIONS
Consider the function f ( x )  1/ x
Solution
It is a continuous function because it is continuous at every
point of its domain. However, it has a point of discontinuity
at x  0 because it is not defined there.
4
2
0
-4
-2
-2
-4
0
2
4
2.3 Continuity (13)
Continuous Functions
• Polynominal functions f are continuous at every real
number c because limx → c, f(x) = f(c).
• Rational functions are continuous at every point of
their domains. They have points of discontinuity at
the zeros of their denominators.
• The absolute value function y = |x| is continuous at
every real number.
• The exponential, logarithmic, trigonometric functions
and radical function like y = x (1/n) (n = a positive
integer greater than 1) are continuous at every point
of their domains.
2.3 Continuity (14, Theorem 6)
Algebraic Combinations
Theorem 6 Properties of Continuous Function s
If the functions f and g are continuous at x  c , then the
following combinations are continuous at x  c .
1. Sums :
f g
2. Difference :
f g
3. Products :
f g
4. Constant multiples :
5. Quotients :
k  f , for any number k
f / g , provided g (c )  0
2.3 Continuity (15, Theorem 7)
Composites
Theorem 7 Composite of Continuous Function s
If f is continuous at c and g is continuous at f (c ), then
the composite g f is continuous at c .
g f
continuous at c
g (x )  sin x 2
continuous
at f(c)
c continuous
at c
f (x )  x 2
f(c)
g(f(c))
g (f (x ))  sin x 2
2.3 Continuity (16, Example 4)
Composites
Example 4 USING THEROREM 7
x sin x
Show that y  2
is continuous
x 2
Solution
The function is continuous by letting
x sin x
g (x ) | x |, f (x )  2
x 2
0.4
0.3
0.2
0.1
0
-8
-4
0
4
8
2.3 Continuity (17, Theorem 8)
Intermediate Value Theorem for Continuous Functions
Theorem 8 The Intermediate Value Theorem for
Continuous Functions
A functions y  f ( x ) that is continuous on a closed interval
a , b  takes on every value between f (a ) and f (b ). In other
words, if y 0 is between f (a ) and f (b ), then y 0  f (c ) for
some c in a , b .
f(b)
yo
f(a)
a
c
b
2.3 Continuity (18, Example 5)
Intermediate Value Theorem for Continuous Functions
Example 5 USING THEROREM 8
Is any real number exactly 1 less than its cube ?
2.4 Rates of Change and Tangent Lines (1)
Average Rates of Change
• The average rate of change of a quantity over a
period of time is the amount of change divided by the
time it takes. Such as average speed, grows rate
of populations, monthly rainfall.
• In general, the average rate of change of a function
over an interval is the amount of change divided by
the length of the interval.
y
dy
Rate of change 
dx
f(x)
dy
dx
x
2.4 Rates of Change and Tangent Lines (2)
Average Rates of Change (Example 1)
Example 1 FINDING AVERAGE RATE OF CHANGE
Find the average rate change of f (x )  x 3  x over the
interval [1, 3].
Solution
rate of change 
f (3) - f (1)
3 -1
60
24 - 0

 12
2
40
20
0
-20
-4
-2
0
2
4
2.4 Rates of Change and Tangent Lines (3)
Average Rates of Change (Example 2-1)
Example 2 GROWING DROSOPHILA IN A LABORATORY
Ue the point P (23, 150) and Q (45, 340) to computer the
average rate of change and the slope of the secant line PQ
Solution
average rate of change
p 340  150


t
45  23
 8.6 flies/day
2.4 Rates of Change and Tangent Lines (4)
Average Rates of Change (Example 2-2)
Example 2 GROWING DROSOPHILA IN A LABORATORY
Ue the point P (23, 150) and Q (45, 340) to computer the
average rate of change and the slope of the secant line PQ
Solution
the secant slope
p 340  150


t
45  23
 8.6 flies/day
an average rate of
change as the slope
of a secant line
2.4 Rates of Change and Tangent Lines (5)
Average Rates of Change (Example 2-3)
Example 2 GROWING DROSOPHILA IN A LABORATORY
In additional, we may want to know how fast the population
was growing on day 23 itself.
Solution
to find out, we can watch the
slope of the secant PQ change
as we back Q along the curve
toward P .
Q
(45,340)
(40,330)
slope PQ
(340-150)/(45-23)  8.6
(330-150)/(40-23)  10.6
(35,310)
(30,265)
(310-150)/(35-23)  13.3
(265-150)/(30-23)  16.4
2.4 Rates of Change and Tangent Lines (6)
Average Rates of Change (Example 2-4)
Example 2 GROWING DROSOPHILA IN A LABORATORY
In additional, we may want to know how fast the population
was growing on day 23 itself.
Solution
In terms of geometry, as Q approaches P along the curve is :
The secant PQ approaches the tangent line AB that we drew
by eye at P .
This means that within the limitations
of our drawing, the slopes of the
secants approach the slop of the
tangent
350-0
 17.5 flies/day
35-15
2.4 Rates of Change and Tangent Lines (7)
Tangent to Curve
• The rate at which the value of the function y = f(x) is
changing with respect to x at any particular value x =
a to be the slope of the tangent to the curve y = f(x) at
x = a.
• Are we to define the tangent line at an arbitrary point
P on the curve and find its slope from the function y =
f(x) ? Our usual definition of slope requires two
points
2.4 Rates of Change and Tangent Lines (8)
Tangent to Curve
The procedure to find the slope of a point P is
follows :
1. We start with what we can calculate, namely, the
slope of a secant through P and a point Q nearby
on the curve.
2. We find the limiting value of the secant slope (if it
exists) as Q approaches P along the curve.
3. We define the slope of the curve at P to be this
number and define the tangent to the curve at P to
be the line through P with this slope.
2.4 Rates of Change and Tangent Lines (9)
Tangent to Curve (Example 3-1)
Example 3 FINDING SLOPE AND TANGENT LINE
Find the slope of the parabola y  x 2 at the point P (2,4).
Write this tangent line equation.
Solution
consider point P (2, 4) and a nearby point
Q (2  h , (2  h )2 ).
Q(2+h, (2+h)2)
P(2,4)
-1
0
1
2
3
4
2.4 Rates of Change and Tangent Lines (10)
Tangent to Curve (Example 3-2)
Solution (y  x 2 )
consider point P (2, 4) and a nearby point Q (2  h , (2  h )2 ).
y
secant slope 
x
(2  h )2  4

h 4
4
secant slope is
(2  h )2  4
h 4
4
Q(2+h, (2+h)2)
tangent slope  4
y  (2  h )2  4
P(2,4)
x  h
-1
0
1
2
3
4
2.4 Rates of Change and Tangent Lines (11)
Tangent to Curve (Example 3-3)
Solution (y  x 2 )
The limit of the secant slope as Q appooaches P along
the curve is
secant slope is
lim (secant slope)  lim(h  4)  4
Q P
(2  h )2  4
h 4
4
h 0
the slope at P is 4
and the line equation
y  4x - 8
Q(2+h, (2+h)2)
tangent slope  4
y  (2  h )2  4
P(2,4)
x  h
-1
0
1
2
3
4
2.4 Rates of Change and Tangent Lines (12)
Slope of a Curve
Definition Slope of a Curve at a Point
The slope of the curve y  f ( x ) at the point P (a ,f (a )) is the
number
f (a  h )  f (a )
,
h 0
h
m  lim
provided the limit exists.
y
y=f(x)
Q(a+h, f(a+h))
f(a+h)-f(a)
P(a, f(a))
h
a
a+h
x
2.4 Rates of Change and Tangent Lines (13)
Tangent to Curve (Example 4-a)
Example 4 EXPLORING SLOPE AND TANGENT
Let f (x )  1/ x (a) Find the slope of the curve at x  a
(b) Where does the slope equal -1/4 ?
(c) What happens to the tangent to the curve at the
point (a , 1/ a ) for different values of a ?
Solution
(a) The slope at x  a is
1
1
f (a  h )  f (a )
1
1
a h  a
lim
 lim
 lim
 2
h 0
h 0
h 0 a (a  h )
h
h
a
2.4 Rates of Change and Tangent Lines (14)
Tangent to Curve (Example 4-b)
Example 4 EXPLORING SLOPE AND TANGENT
Let f ( x )  1/ x (b) Where does the slope equal -1/4 ?
Solution
(b) The slope will be  1/ 4 if
1
1
 2 
a
4
 a  2
-4
-2
0
2
4
2.4 Rates of Change and Tangent Lines (15)
Tangent to Curve (Example 4-c)
Example 4 EXPLORING SLOPE AND TANGENT
Let f (x )  1/ x
(c) What happens to the tangent to the curve at the point (a , 1/ a ) for
different values of a ?
Solution
The slope  1/ a 2 is always negtive.
As a  0+ , the slope approaches - and the tangent becomes
increasingly steep.
As a move away from the origin in either direction, the slope
approaches 0 and the tangent becomes inreasingly horizontal.
-4
-2
0
2
4
2.4 Rates of Change and Tangent Lines (16)
Tangent to Curve
ALL of these are the same :
the slope of y  f ( x ) at x  a
the slope of the tangent to y  f ( x ) at x  a
the (instantaneous) rate of change of f ( x ) with
respect to x at x  a
f (a  h )  f (a )
lim
h 0
h
2.4 Rates of Change and Tangent Lines (17)
Normal to a Curve (Example 5)
Example 5 FINDING A NORMAL LINE
Write an equation for the normal to the curve
f (x )  4  x 2 at x  1
Solution
The slope at x  1 is
f (1  h )  f (1)
4  (1  h )2  3
lim
 lim
h 0
h 0
h
h
h (2  h )
 lim
 2
h 0
h
The normal line at x  1
-3
-2
5
1
y  2x  2
-1
0
1
2
3
2.4 Rates of Change and Tangent Lines (18)
Speed Revisited (Example 6)
• A body’s average speed along a coordinate axis for
a given period of time is the average rate of change
of its position y = f(t).
• Its instantaneous speed at ant time t is the
instantaneous rate of change of position with
respect to time at time t.
Example 6 INVESTIGAING FREE FALL
A falling rock position with f (t )  16t 2 , Find the speed
at t  1.
Solution
f (1  h )  f (1)
16(1  h )2  16(1)2
The speed is  lim
 lim
h 0
h 0
h
h
 lim16(h  2)  32
h 0