# Thread: Need help solving this problem. (Inverse Functions)

1. ## Need help solving this problem. (Inverse Functions)

Can anyone show me how to solve this?
g(x) = 10x^9 + 5x^3

10(g^-1(11))^9 + 5(g^-1(11))^3-9

2. ## Re: Need help solving this problem. (Inverse Functions)

What do you have to solve? (I can't see anything, maybe I'm the only one)

3. ## Re: Need help solving this problem. (Inverse Functions)

i posted a screenshot of the problem but i guess it didnt work. i wrote it out above

4. ## Re: Need help solving this problem. (Inverse Functions)

Originally Posted by bseymore
Can anyone show me how to solve this?
g(x) = 10x^9 + 5x^3

10(g^-1(11))^9 + 5(g^-1(11))^3-9
$\displaystyle g(x) = 10x^9 + 5x^3$

let $\displaystyle a$ be the real value such that $\displaystyle g(a) = 11$

since $\displaystyle g(a) = 11$ , $\displaystyle g^{-1}(11) = a$

$\displaystyle 10a^9 + 5a^3 - 9 = g(a) - 9 = 11 - 9 = 2$

5. ## Re: Need help solving this problem. (Inverse Functions)

Originally Posted by bseymore
Can anyone show me how to solve this?
g(x) = 10x^9 + 5x^3

10(g^-1(11))^9 + 5(g^-1(11))^3-9
For any (invertible) function g, $\displaystyle g(g^{-1}(x))= x$

Note that $\displaystyle 10x^9+ 5x^3- 9= g(x)- 9$.

6. ## Re: Need help solving this problem. (Inverse Functions)

thanks guys! I understand it now