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# Writing a function rule

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## Mitsouka Jean-Claude

on 3 May 2016

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#### Transcript of Writing a function rule

Lesson 4.4:
Writing a Function rule

Introduction:
A function rules is an equation used to describe a function; or what you plug into x to get y.
The function rule is the equation that describes the relationship between the input and output.
x (input)
y (output)
Function rule (machine):
An the equation that turns
the x (input) into y (output)
Demonstration:
X
0
2
4
6
F(x)
3
5
7
9
Example 1
When writing a function rule, just ask yourself how can I get:
0 to 3
2 to 5
4 to 7
6 to 9
The Function Rule is:
f(x)= x + 3
Example 2
X
0
1
3
5
Y
0
3
9
15
Check your work by pluging in numbers into f(x)= n+3
3= 0+3; yes
5= 2+3; yes
7= 4+3; yes
9= 6+3; yes
Again, ask yourself how to get:
0 to 0
1 to 3
3 to 9
5 to 15
The answer to this example is
f(x)= 3n
f(x)= 3n
0= 3(0)
3= 3(1)
9= 3(3)
15= 3(5)
Example 3
Write a function rule for this situation
You get paid \$10 for each good grade you get on a test.
Paying attention to key words, you can conclude that:
The output is how much you get paid
The input is how much good grade test you get
So the function is: f(g)= \$10g
Question 3.1: how much are you paid if
you get 3 good grades on a test
Plug 3 (the number of test), which is the g (or x)
variable into the function rule to get:
f(g)= \$10(3) and then \$30
Pre-Reqs
Before starting the demonstrations, you will have to now that we will be writing function rules off of table of values and situations.
The format for a function rule (for now)
is y= (function rule) x
Also that f(x) = the function of x
f(c)= the function of c
f(z)= the function of z
Problems
Problem 1:
Solve:
X
-3
-1
1
3
F(X)
-1
1
3
5
Problem 2:
Solve
X
0
3
6
9
F(X)
0
6
12
18
Guided Problems
x
-5
0
1
4

f(x)
13
-2
-5
-12

Problem 1
Problem 2
x
-3
0
1
5

f(x)
-10
-1
2
14

Problem 3
Write an equation to represent this situation:
The weight of a bag of candy depends on how much pieces of candy you have when each piece of candy weighs .15 lbs.

How much would a bag of candy weigh if there was 5 pieces of candy?

Problem 4
Write an equation to represent this situation:
The amount of pizza that a bro would bring to a party depends on 3 times as much bros at the party divided by eight.

Problem 3
Solve:

X
-3
0
1
4

F(X)
.5
2
2.5
4

Problem 4
Write an eauation to represent this situation:
The amount you get paid for a job that pays \$15 for every hour.

How much would you get paid after you work for 8 hours?

Problem 5
Example 4
Write a situation that models the equation:
y= 3+x
Pay attention to the positions of the variable, y is the dependent variable and x is the independent vairable.
So...
That means that 3+x is the function
So let your creativity flow and your mind wander to solve this problem.
Write an equation to represent this situation:
A man gets rewarded 5 dollars for every time he walks to work.

How many dollars does he receive after walking to work 17 times.
Agenda
SPEAK OUT
Pre-Req
Demonstrations
Guided problems
Practice Problems

Problem 6
Write a situation that represents this equation:
f(x)= 100x

When solving a function rule, just remember that the function rule is the equation in the format y=_____ x
Example: if the funxtion rule was y=7+x, and x was 3, y would equal 10
APRIL , 2016
SPEAK OUT: 1. Given the functions: f(x)= 5x-2 and g(x)= 2x+5
Evaluate the following:
a. f(2)-g(3)

CQ: How can we understand the symbols and notation of function?
Today's topic: Writing a function rule
April 15, 2016
CQ: How do we master our function unit?
Today's Goal:
Group A and B- Function Quiz
Group C- Function transformation
SPEAK OUT: Write a relation that is a function, one that is not a function
April 19, 2016
CQ: How can we use our knowledge of functions to explore transformation?
Today's Goal:
Group A and B- Delta Math Mastery sheet
Group C- Transformation
May 3, 2015
SPEAK OUT: Evaluate the following function:
f(x)= x-3 g(x)= 3x+2
a. f(10) b. g(6) c. f(2) * g(6)
CQ: How can we use our knowledge of functions to explore transformation?
Full transcript