1. Power Functions
Unit 4 Day 7

2. Warm-Up 1) (a7)(a4) = _________ 2) (2p3)(5p)= _______________
3) (x4y5)2= _______________
4) (2x3y4)2= _______________

3. Warm-Up Answers a7+4 = a11 1) (a7)(a4) = _____________________
2●5●p =10p4
(x4●2 )(y5●2) = x8y10
OR (x4y5)(x4y5)
(22)(x3●2)(y4●2) = 4x6y8
OR (2x3y4)(2x3y4)
1) (a7)(a4) = _____________________
2) (2p3)(5p)= _____________________
3) (x4y5)2= _______________________
4) (2x3y4)2= ______________________

4. Homework Answers
Domain: All real numbers
Range: y > -1

5. Homework Answers
Domain: All real numbers
Range: y ≥ 2

6. Homework Answers Domain: -4 ≤ x ≤ 6 Range: -4 ≤ y ≤ -1 or 0 ≤ y ≤ 6
NOTE: even though this says “or” you MUST include BOTH parts of the range!!

7. Homework Answers

8. Homework Answers

9. Homework Answers 6)

10. Homework Answers

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12. Notes: Power Functions
If you miss filling in part of the notes, get the ones you miss from Blackboard! 

13. Power Function Definition What effect will the k have? for k < 1
Vertical stretch or compression
for k < 1

14. Special Power Functions…let’s draw a reminder of their basic shapes! 
Parabola
y = x2
Cubic function
y = x3
Hyperbola
y = x-1
Draw pictures in your notes!

15. Special Power Functions…let’s draw a reminder of their basic shapes! 
y = x-2
Draw pictures in your notes!

16. Special Power Functions
Most power functions are similar to one of these six
xp with positive even powers of p are similar to x2
xp with positive odd powers of p are similar to x3
xp with negative even powers of p are similar to x -2
xp with negative odd powers of p are similar to x -1
Draw pictures in your notes!

17. Special Power Functions
Which of the functions have symmetry? What kind of symmetry?
xp with positive even powers of p are similar to x2
Symmetry across y-axis
xp with positive odd powers of p are similar to x3
Symmetry about the origin (or 180˚ rotation)
(symmetry across x-axis, then y-axis)
xp with negative even powers of p are similar to x -2
xp with negative odd powers of p are similar to x -1

18. This is a power function
Direct Proportions
The variable y is directly proportional to x when: y = k * x
k is some constant value – called constant of proportionality
Alternatively
As x gets larger, y must also get larger
keeps the resulting k the same
This is a power function

19. Direct Proportions Examples: Distance = rate x time
Force = mass x acceleration
Paycheck = ($8)·(# of hrs worked)
Test grade = (5 pts/question)·(# of questions correct)
The harder you hit the baseball, the farther it travels
Distance hit is directly proportional to the force of the hit

20. Direct Proportion Suppose the constant of proportionality is 4
Then y = 4 * x
What does the graph of this function look like?
Remember
y = 4x is in y = mx + b form so
b = y-int is (0, 0)
and
m = slope is 4 or 4/1

21. Again, this is a power function
Inverse Proportion
Another type of power function is an inverse proportion
k is some constant value – called constant of proportionality
Alternatively y = k * x -1
As x gets larger, y must get smaller to keep the resulting k the same
Again, this is a power function

22. Inverse Proportion Example:
The time taken for a journey is inversely proportional to the speed of travel
The time needed to dig a hole is (approximately) inversely proportional to the number of people digging
Time to bake cookies is inversely proportional to oven temperature
If you bake cookies at a higher oven temperature, they take less time

23. Remember we graphed these a few days ago! 
Inverse Proportion
Remember what the graph looks like
Let the constant or proportionality k = 4
Then
Remember we graphed these a few days ago! 
Left
Branch ½ -½
Right
Branch ½ ½

24. Formulas for Power Functions
Say that we are told that f(1) = 7 and f(3)=56
We can find f(x) when linear y = mx + b
We can find f(x) when it is y = a(b)t
Now we consider finding f(x) = k xp
We’ll use the calculator for now!

25. Application – Power Regression! Cycling for 24 miles
Rate (miles/hr) 1 3 6 9 12 18 24
Time (hr) 8 4 2
Graph the points.
Find a power function that models the data. 12 11 10 9 8 7 6 5 4 3 2 1
Press STAT then EDIT
and type in
L1 L2
Time (hr)
Press STAT then CALC
then pick A: PwrReg
*Remember to enter L1, L2, Y1 behind it!
Rate (miles/hr)
y = 24●x-1 OR y = 24/x

26. Application – Power Regression! Cycling for 24 miles
Rate (miles/hr) 1 3 6 9 12 18 24
Time (hr) 8 4 2
Graph the points.
3. Determine whether the function is direct or inverse variation. 12 11 10 9 8 7 6 5 4 3 2 1
Inverse variation because as x-values increase, y-values decrease.
ALSO, inverse variation because y = 24●x-1
fits y = k●x-1
Time (hr)
Rate (miles/hr)

27. Application – Power Regression! Cycling for 24 miles
Rate (miles/hr) 1 3 6 9 12 18 24
Time (hr) 8 4 2
/ /3
Graph the points.
Fill in the missing values in the table 12 11 10 9 8 7 6 5 4 3 2 1
*see above*
Get from table in calculator OR do Y1(1) then Y1(9) etc on main screen
Time (hr)
5. Determine the rate of cycling if a person biked for 6 hours.
In y=, do y2 = 6
then find intersection with 2nd Trace 5.
4 miles per hour
Rate (miles/hr)

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29. Quiz time!