So this tells us that x is equal to pi over four when y is equal to pi over four. And so we know that this is pi over four as well. So let me just rewrite this because it's getting a little bit messy. So we know that five times cosine of pi over four minus dy dt, the derivative of y with respect to t, which is what we want to figure out, times sine of pi over four is equal to zero. Is equal to zero, and let me put some parentheses here just to clarify things a little bit. All right, so let's see. Now it's just a little bit of algebra.