# Thread: help algebra 2 functions

1. ## help algebra 2 functions

f(x) 2x+1, g(x)=2x^2+x

determine (gf)(3)

ok so i dont know where to go since this is an online class

g(f(3)?
g(2(3)+1 = 7?
g(7)?
so confused someone please do this step by step i especially dont know how to do these when there are exponents like the 2x^2

2. Originally Posted by siberianfog
f(x) 2x+1, g(x)=2x^2+x

determine (gf)(3)

ok so i dont know where to go since this is an online class

g(f(3)?
g(2(3)+1 = 7?
g(7)?
so confused someone please do this step by step i especially dont know how to do these when there are exponents like the 2x^2
$\displaystyle g[f(3)] = g[2(3)+1] = g(7) = 2(7)^2 + 7 = 2(49) + 7 = 98 + 7 = 105$

3. wow thank you i have been getting them done fast now, 1 more pleasE? its very very very appreciated.

f(x) 2x+1, g(x)=2x^2+x
determine (fg)(x+1)

4. Originally Posted by siberianfog
wow thank you i have been getting them done fast now, 1 more pleasE? its very very very appreciated.

f(x) 2x+1, g(x)=2x^2+x
determine (fg)(x+1)
$\displaystyle f[g(x+1)] = f[2(x+1)^2+(x+1)] =$ ... you finish it.

5. 2(x^2+1)+(x+1)
2x^2+2+x+1
2x^2+3+x

I GOT
2(2x^2 + 3 + x) = 4x^2 + 6 + x

but the book says thats wrong

4x^2+10x+7? dont know where you get that

6. 2(x^2+1)+(x+1)
... note that $\displaystyle (x+1)^2 \ne x^2+1$

7. where do i go wrong?

2(x^2 + 1) + (x+1)
2x^2 + 2 + x + 1
2x^2 + 3 + x

2(2x^2 + 3x + x)
4x^2 + 6x + 2x + 1
4x^2 + 8x + 1

8. once again ... $\displaystyle 2(x+1)^2 + (x+1) \ne 2(x^2+1) + (x+1)$

specifically ... $\displaystyle (x+1)^2$ does not equal $\displaystyle (x^2+1)$

I recommend you research how to square a binomial.

9. Thank you