# What is the derivative for arctan(2/x)?

1. Jun 17, 2005

### EvLer

What is the derivative for

arctan(2/x)?

I know it's generally: [(1/a)arctan(x/a)]' = 1/(x^2 + a^2); but in my case its x^-1!

Thanks for any help.

2. Jun 17, 2005

### quasar987

The formula to remember is

$$Arctg'(x) = \frac{1}{1+x^2}$$

So using the chain rule,

$$Arctg'(f(x)) = \frac{f'(x)}{1+[f(x)]^2}$$

which gives the derivative of Arctg for any argument.