Transcript Function rules and Other Cool Math Stuff

Function rules and Other Tight
Math Stuff
Mr Streety’s 7th Grade Class
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Writing function rules from tables
 Writing tables from Function rules
 Graphing Tables and Function rules
 Writing Function Rules from Graphs
Function Rules from Tables
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There are two ways to
write a function rule
for a table
 The first is through
number sense.
 This is the Harder of
the two
Function rules from tables
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When X=0, what does
Y=?.
This gives you the first
part of your function
y=x+2
After you find what Y=
when X=0, you need to
subtract this number from
the following values for Y
Apples and Bananas Function
Rule
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As you know we start
with the equation:
 y=Ax+B
Where A and B are
constant numbers, and
of course x and y are
variables meaning
their value changes
with the table.
Apples and Bananas
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The first step here is to
solve for B, using the
first set of numbers
from the table
y=Ax+B
2=A(0)+B
B=2
This gives us the new
equation y=Ax+2
Apples and Bananas Function
Rule
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The second step is to
use our new equation
to find a value for A
Y=Ax+2
5=A(1)+2
5-2=A(1)+2-2
3=A(1)
A=3
Apples and Bananas Function
Rule
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Now we have our new
equation
y=3x+2
We can plug our x
values in to check the
equation
y=3(2)+2
Y=6+2
Y=8
Mrs. Robinson's Lawn
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We have been hired to mow Mrs.
Robinson's lawn. She is going to give us a
two dollar bonus for starting early. In
addition to this she will pay us 3 dollars an
hour.
 What is the function rule for this problem?
Writing Tables from Function
Rules
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Since 2 dollars is a
bonus, we get that as
soon as we start. We
get 3 dollars an hour
after that.
 Y=3x+2
 First we can choose
any values for x we
want unless they are
given to us.
Tables From Function Rules
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The next step is to
plug these values in
for the variable x in
our equation.
 Y=3x+2
 Y=3(0)+2
 Y=2
Tables From Function Rules
Now let’s try the next
set of numbers.
 y=3(1)+2
 y=5
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Tables from Function Rules
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As you plug in the rest
of the values for x,
you will get the
corresponding values
for y.
Graphing Tables and Function
Rules
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First of all if you only
have a function rule
you need to make a
table which we just
covered.
 From the table to the
left we make a graph
Mrs. Robinson's Lawn
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We will need to plot
the set of numbers as
they as they appear in
the table.
 For the first set of
numbers we will go 0
to the right and up 2
 For the next set of
numbers we will go 1
to the right and 5 up
Mrs. Robinson's Lawn
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Mowing Lawns
y-axis (dollars)
Of course this is just
the first two sets of
numbers.
 Let’s see what
happens if we plot the
rest of the numbers
16
12
8
4
0
0
1
2
3
x-axis (hours)
4
5
Mrs. Robinson's Lawn
After plotting all the
points we can draw a
line from point to
point that will help us
find values between
the points.
Mowing Lawns
y-axis (dollars)
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16
12
8
4
0
0
1
2
3
x-axis (hours)
4
5
Mrs. Robinson's Lawn
Using the line we can
tell how much money
we can make mowing
her lawn for 2 and a
half hours or or four
and a half
Mowing Lawns
y-axis (dollars)
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16
12
8
4
0
0
1
2
3
x-axis (hours)
4
5