what would be integral [cot(x)]dx where x goes from 0 to pi?

the answer is -pi/2

This question is from AIEEE 2009.

The solution is right here but i cant understand the solution...can anybody explain..??

http://www.narayanagroup.com/aieeeqps/2009.pdf its on page 13 question 70.

Wolfram alpha was unable to solve this...