# Euler's formula question

1. Nov 10, 2012

### DiracPool

If e^iPi/2=i, what does e^-iPi/2 equal? And could you please write it out in cos + sin notation? For some reason I am not geting this. This is not homework, by the way, its come up in an article on spinors I'm reading Thanks.

2. Nov 10, 2012

### Klungo

A simple google check would do the trick.

Anywho, e^(ix)=cos(x)+i*sin(x) for complex variable x.

3. Nov 10, 2012

### micromass

Staff Emeritus
Continuing with this. If $x=-\pi /2$, then

$$e^{-i\pi /2}=\cos(-\pi/2)+i\sin(-\pi/2)=-i.$$

4. Nov 10, 2012

### DiracPool

I got the first one Klungo. Thanks for the follow up micromass. Now I got it, its just like spinning the dial from the top of the complex plane to the bottom.