# inverse function derivative

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• February 5th 2007, 12:46 AM
gracy
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

my answer :1/2
• February 5th 2007, 01:14 AM
ticbol
Quote:

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

my answer :1/2

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.
• February 5th 2007, 01:16 AM
earboth
Quote:

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

my answer :1/2

Hello, Gracy,

your answer is correct.

f is a linear function therefore the inverse of f is a linear function too:

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

EB