# Thread: Need help with F o G and G o F

1. ## Need help with F o G and G o F

Why did I get this wrong

I factored it to
(4x-3)(4x-3)-2
which gives me
16x^2+8x-9-2
16x^2+8x-11

2. ## Re: Need help with F o G and G o F

Your link is broken on my machine, please type the equations in case other users find the same.

3. ## Re: Need help with F o G and G o F

$f(x) = x^2-2$

$g(x) = 4x-3$

$f[g(x)] = (4x-3)^2 - 2$

note that $(4x-3)^2 \ne 16x^2+8x-9$

you need to learn how to square a binomial

4. ## Re: Need help with F o G and G o F

What did I do wrong?

5. ## Re: Need help with F o G and G o F

Originally Posted by GaDoomZ

Why did I get this wrong

I factored it to
(4x-3)(4x-3)-2
which gives me
16x^2+8x-9-2
16x^2+8x-11
$f\circ g(x)=(4x-3)^2-2$
$g\circ f(x)=4(x^2-2)-3$

6. ## Re: Need help with F o G and G o F

Originally Posted by GaDoomZ
What did I do wrong?
I told you ... you did not square the binomial $(4x-3)^2$ correctly.

7. ## Re: Need help with F o G and G o F

Originally Posted by skeeter
I told you ... you did not square the binomial $(4x-3)^2$ correctly.
Ah I see what I did wrong,

16x^2 - 24x + 7

thanks