Question

Points of y=f(x) are:
A (-1,0)
B (2,1)
C (5, 0)

Determine the new points for y=f(4x)

Answer 1

A (-4,0)
B (8,4)
C (20,0)

Answer 2

Multiply domain by 4
A y = f(-4)
B y = f(8)
C y = f(20)

there is not enough information to know the y-values

Answer 3

If it helps, I found out what the original function is: -1/9(x-2)^2+1. At least I think that's right

Answer 4

yeah that would help
so if you know f(x), replace x with 4x to get f(4x)
--> -1/9(4x-2)^2 +1

Answer 5

Apparently the y values are the same as the original, but the x values aren't what you say. I've tried (-4, 0) (8, 1) (20, 0) and I'm told its wrong.

Answer 6

Apparently I'm suppose to divide by 4. Does that make sense?

Answer 7

yeah it does, im trying to work out the new equation
so it should be
(-1/4,0)
(1/2,1)
(5/4,0)

Answer 8

Can you explain why it works? I don't understand.

Answer 9

yeah when you replace x with 4x in the equation as i did above
-> f(4x) = -1/9(4x-2)^2 +1
well the new vertex is at point where 4x-2 = 0 because standard form is a(x-h)^2 +k
4x-2 =0 -> 4x = 2 -> x = 1/2
vertex: (1/2, 1)

Answer 10

for the others plug in 0 for y
-1/9(4x-2)^2 +1 = 0
-1/9(4x-2)^2 = -1
(4x-2)^2 = 9
4x-2 = +-3
4x = +-3 +2
x = (+-3 +2)/4
x = -1/4, 5/4

Answer 11

Alright, I get it now. Thanks a lot.

Answer 12

no problem