Question

If the range of the function f(x) = 4 − 4x is {-20, -16, -8, 0, 4}, what is its domain?




A{0, 1, 2, 4, 6}



B{2, 3, 5, 6, 7}



C{1, 3, 5, 7, 9}



D{0, 1, 3, 5, 6}

Answer 1

Pick a value out of the range, say 4

plug 4 into f(x) to get

f(x) = 4 − 4x

4 = 4 − 4x

now solve for x to get x = ??

Answer 2

I still don't get it...I plugged the 4 in for f(x) but got 21.

Answer 3

solve 4 = 4 − 4x for x and tell me what you get

Answer 4

0

Answer 5

so if you were to plug x = 0 into f(x) = 4 − 4x, you'd get 4

when x = 0, f(x) = 4

Answer 6

I'm going backwards because they give you the range (which is the set of y values or outputs)

Answer 7

so you have to figure out which x values give you those specific y values

Answer 8

I still honestly don't understand..

Answer 9

The range is {-20, -16, -8, 0, 4}

Answer 10

there are specific values of x that produce those y values

Answer 11

when x = 0, y is

y = 4 − 4x

y = 4 − 4(0)

y = 4 - 0

y = 4

So the input of x = 0 produces the output y = 4

Answer 12

What is the input when the output is y = -8 ?