# Math Help - inverse function derivative

1. ## inverse function derivative

find the value of d/dx(f^-1(x)) at x=2 when f(x)=2x-4
(a)3
(b)1/3
(c)1/2
(d)1/6

2. Originally Posted by gracy
find the value of d/dx(f^-1(x)) at x=2 when f(x)=2x-4
(a)3
(b)1/3
(c)1/2
(d)1/6

Yes, 1/2 is correct.

That is easy.
How come you were asking for the inverse of a cubic function before? That one is super hard. You have to use the Cubic Formula there.
For Linear and Quadratic functions, getting their inverses, if they exist, is relatively easy.

3. Originally Posted by gracy
find the value of d/dx(f^-1(x)) at x=2 when f(x)=2x-4
(a)3
(b)1/3
(c)1/2
(d)1/6

$f^{-1}:\ y=\frac{1}{2}x-2$. The derivative of this function is a constant: 1/2.