Ok so I have to make up a trig identity

The instructions are to start with a statement that I know is true, and than keep changing both sides to equivalent equations until it is complex

So far I have:

cos²x = cos²x

1-sin²x = cos2x + sin²x

I need 2 more lines of changing them until the final identity..

But I don't know how to keep going!

Any help?

Thanks