Let's verify the identity . What is a good first step?

In this next part, we'll use a trick: add and subtract to the numerator in the right-hand side. What do you get for your new right-hand side?

What do we get when we simplify the right-hand side?

What do you get when you multiply the fraction in the right-hand side by and simplify?

Let's simplify the previous expression and figure out what equation we are working with now. What do we have?

How can we finish the proof?