I need to prove the following identity:
I am able to prove that the left side of the equation is equal to:
The obvious difference between what I am able to prove and what the identity actually says is the difference in sign between tan x and tan y in the denominator.
I'll be happy to explain how I arrived at my proof, but I'm hoping it should be pretty straight forward to understand.
So my question is this:
Is there some way to prove this identity, or is this a false identity (perhaps a misprint in the text I'm reading)?