Hey, can someone help me find the primitive of:

$\displaystyle cosec^2x$

the answer is $\displaystyle -cotx + c$

EDIT: $\displaystyle \int cosec^2 x $

$\displaystyle \int sec^2(90-x)$

$\displaystyle = tan(90-x)+ c$

$\displaystyle = cotx + c $

But how did they get - cotx

Thanks in advance