Dividing by 1 never hurt anyone. We could say that this is the same thing as cosine squared y. I'm really doing this to see if I can start to express it as some type of a rational expression, which might involve, at some point, a sine divided by a cosine, and I could have a tangent. Let's divide by 1. We know from the Pythagorean identity that 1 is equal to sine squared of y plus cosine squared of y. Let's write that. We could write cosine squared of y plus sine squared of y. Once again, why was I able to divide by this expression?