# I Derivative with respect to 1/x

1. Nov 14, 2016

### flower321

if (d/dx) cos(x) = -sin(x) then (d/d{1/x}) cos(x) = ? i.e. the derivative of cos(x) with respect to 1/x

2. Nov 14, 2016

### BvU

You can subsitiute $\ y = {1\over x}\$ and use the chain rule to determine the derivative of $\cos\left ( 1\over y \right )$.