Inverse functions calculus question?

Question

abbles · Answer

Last one!  It says that f'(x) and g'(x) are inverses.  f(x) = 4x^3 - 7/x + 5
Find g(8)

abbles · Answer

I know that g'(x) = 1/f'(g(x))
But I need to know g(8) first I guess.. and I can't recall how to find that o.O

satellite73 · Answer

i think you don't need that

satellite73 · Answer

oh wait, it says the derivatives are inverses??

abbles · Answer

Actually it might have been f(x) and g(x)... I might have written it down wrong

satellite73 · Answer

that would be my guess 
can you check?

abbles · Answer

It was a problem on the board in class, no way for me to check it :/ I wrote it down as f'(x) and g'(x)... but I do think it was f(x) and g(x) are inverses.

satellite73 · Answer

yeah i am lost 
could  you have been asked for $g'(8)$ because honestly i cannot figure out how you can recover $g(8)$ from all this 
let me think

satellite73 · Answer

$$f(x) =\frac{ 4x^3 - 7}{x + 5} $$right?

satellite73 · Answer

so to find $g(8)$ is same as solving $$\frac{4x^2-7}{x+5}=8$$ which is not really possible

abbles · Answer

The 5 is on the top!  Only the 7 is being divided by 5
:)

abbles · Answer

*by x

abbles · Answer

$$f(x) = 4x^3 - \frac{ 7 }{ x } + 5$$

abbles · Answer

sorry lol

abbles · Answer

Still there @satellite73 ?

agent0smith · Answer

Close it and start again so it's easier to follow :P

abbles · Answer

Kay xD