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? This expression by the Pythagorean identity, which really comes out of the unit circle definition of trig functions, this is equal to 1, so I have not changed the value of this expression. What makes this interesting is if I want to introduce a sine divided by a cosine, I could just divide the numerator and the denominator by cosine squared. Let's do that.