# Thread: verifying a trigonometric identity

1. ## verifying a trigonometric identity

how would you verify (cosx-cosy)/(sinx+siny) + (sinx-siny)/(cosx+cosy) =0

2. Originally Posted by wolfxpax
how would you verify (cosx-cosy)/(sinx-siny) + (sinx-siny)/(cosx+cosy) =0
Don't forget to use parentheses (as in red above) to make the meaning unambiguous. Also, it looks to me as though one of those – signs should be a +.

Anyway, to prove the identity, put the left side over a common denominator, and see what happens to the numerator.