Transcript ch02.2

For Problems 1-2, we want to find how the volume, V, of a
balloon changes as it is filled with air. We know V(r) = 4/3 πr3,
where r is the radius in inches and V(r) is in cubic inches. The
expression V (3) V (1) represents
3 1
(a) The average rate of change of the radius with respect to the
volume when the radius changes from 1 inch to 3 inches.
(b) The average rate of change of the radius with respect to the
volume when the volume changes from 1 cubic inch to 3 cubic
inches.
(c) The average rate of change of the volume with respect to
the radius when the radius changes from 1 inch to 3 inches.
(d) The average rate of change of the volume with respect to
the radius when the volume changes from 1 cubic inch to 3
cubic inches.
ConcepTest • Section 2.2 • Question 1
ANSWER
(c)
COMMENT:
This is a nice way for students to see the formula and verbal
description for average rate of change together.
ConcepTest • Section 2.2 • Answer 1
For Problems 1-2, we want to find how the volume, V, of a
balloon changes as it is filled with air. We know V(r) = 4/3 πr3,
where r is the radius in inches and V(r) is in cubic inches.
Which of the following represents the rate at which the
volume is changing when the radius is 1 inch?
(a)
(b)
(c)
(d)
V (1.01)  V (1)
 12.69 in 3
0.01
V (0.99)  V (1)
 12.44 in 3
 0.01
 V (1  h)  V (1)  3
lim 
in

h 0
h


All of the above
ConcepTest • Section 2.2 • Question 2
ANSWER
(c). Note that (d) would also be a reasonable
answer because (a) and (b) provide
approximations of the rate of change.
COMMENT:
V (1)  V (0.99)
.
Students should be aware that (b) is equivalent to
0.01
ConcepTest • Section 2.2 • Answer2
For the function g(x) shown in Figure 2.3,
arrange the following numbers in
increasing order.
(a)
(b)
(c)
(d)
(e)
0
g’(-2)
g’(0)
g’(1)
g’(3)
ConcepTest • Section 2.2 • Question 3
ANSWER
(c), (d), (a), (b), (e)
COMMENT:
This can be used as an elimination question in a classroom quiz
session.
ConcepTest • Section 2.2 • Answer 3
Which of the following expressions
represents the slope of a line drawn between
the two points marked in Figure 2.4?
F (a)  F (b)
(a) m 
ab
a
(c) m 
b
F (a)  F (b)
(e) m 
a b
F (b)  F (a )
(b) m 
ba
F (a )  F (b)
(d) m 
ba
ConcepTest • Section 2.2 • Question 4
ANSWER
(b) and (e). The coordinates of the two points
shown are (a, F(a)) and (b, F(b)), so the slope of
the line connecting them is F (b)  F (a)  F (a)  F (b) .
ba
a b
COMMENT:
You could repeat this question drawing the graph of a function
that was increasing between a and b.
ConcepTest • Section 2.2 • Answer 4
Which of the following expressions
represents the slope of a line drawn between
the two points marked in Figure 2.5?
F (x)  F ( x)
(a)
x
F ( x  x)  F ( x)
(c)
x
F ( x  x)  F ( x)
(e)
x  x
F ( x  x)  F ( x)
(b)
x
F ( x  x)  F ( x)
(d)
x  x  x
ConcepTest • Section 2.2 • Question 5
ANSWER
(b). The coordinate s of the two points are ( x, F ( x))
and ( x  x, F ( x  x)), so the slope of the line
connecting them is
F ( x  x)  F ( x) F ( x  x)  F ( x)
m

.
x  x  x
x
COMMENT:
You could repeat this question drawing the graph of a function that
was decreasing between x and x + ∆x.
ConcepTest • Section 2.2 • Answer 5
Let f(x) = x|x|. Then f(x) is differentiable
at x = 0.
(a) True
(b) False
ConcepTest • Section 2.2 • Question 6
ANSWER
2
f
(
h
)

f
(
0
)
h
|
h
|
h


(a). f ' (0)  lim 
. So lim
 lim
0

h 0
h 0
h 0 h
h
h


h|h|
 h2
and lim
 lim
 0. Since the two limits exist
h 0
h 0
h
h
and are equal, then f ( x) is differenti able at x  0.
COMMENT:
Students often associate a minus sign with a number less than 0
rather than a number multiplied by – 1.
ConcepTest • Section 2.2 • Answer 6