(sin(x+y))/cos(x-y)) = cotxcoty/1+cotxcoty

I'm not sure how to verify this

Start by expanding the part on the left.





Then, divide the numerator and denominator by because there is cot over on the right.

Do the same with sin(x).

After doing this... I think you forgot to add a plus sign to your identity... :rolleyes:

Which is in fact: