Posted by **Lucy** on Wednesday, September 17, 2008 at 5:50pm.

I need help with this problem (composite functions):

If f(x) = 4x-3 and h(x )= 4x^2-21, find a function g such that f(g(x)) = h.

I don't understand how we're supposed to combine the functions.

Oh, and the answer is supposed to be g(x) = x^2 - (9/2).

Thanks!

- Math (Grade 12) -
**bobpursley**, Wednesday, September 17, 2008 at 5:55pm
I was reading, and got the answer in my head before I read your answer line.

It is easy.

f(x) is given. 4x-3 YOu want 4x^2-21

so what times 4 will equal 4x^2? Ans x^2

Now what times 4 will equal -21 when you add -3? 4z-3=-21

4z=-18

z=-9/2

so g(x)=x^2 -9/2

- Math (Grade 12) -
**Ahmed**, Wednesday, January 16, 2013 at 12:07pm
4 x 3 = 12

21 – 2 = 19

4 x 2 = 8

5 x 4 = 20

2 + 1 = 3

14 x 12 = 168

4 x 12 = 48

2 + 4 = 6

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