How do you verify the following identity?
#(cos(x) - cos(y))/(sin(x)+sin(y)) + (sin(x)-sin(y))/(cos(x)+cos(y)) = 0#
A helpful starting point when verifying identities involving fractions is to add the fractions. That's what we'll start with here:
As you can see, the binomials in the numerator multiplied very easily because they were differences of squares. Now we rearrange the terms a bit:
Recall the Pythagorean Identity