I'm bored so I'm sharing what I believe is a neat proof for something useful. What you need to know to understand this is derivatives, compositions, and a bit of algebra (I think).
Let g(x) be the functional inverse of f(x).
Using knowledge about functional compositions, I can determine that f(g(x))=x.
Taking the derivative of both sides...
ddx(x)=ddx(f(g(x)))
Solving the derivatives...
1=f′(g(x))g′(x)
Dividing both sides by f′(g(x))...
f′(g(x))−1=g′(x)
f′(g(x))−1=g′(x) is a simple method that allows an indirect derivation of an inverse function.
Example problem:
f(x)=2x2
f′(x)=2x2+1x∗ln(2)
g(x)=√log2(x)
12√log2(x)2+1√log2(x)∗ln(2)=12∗2log2(x)√log2(x)∗ln(2)=12x∗ln(2)√log2(x)=12x√ln(2)∗ln(x)
Now checking the actual derivative of the function I get g′(x)=12x√ln(2)∗ln(x)
I'll upload more proofs when I'm bored again.