So if we want to solve for dh dt, you can multiply both sides by 500. And you get the rate at which our height is changing is equal to 500 times secant squared of pi over 4. That is 1 over cosine squared of pi over 4. Cosine of pi over 4. Let me write this over here. Cosine of pi over 4 is square root of 2 over 2. Cosine squared of pi over 4 is going to be equal to 2 over 4, which is equal to 1 half.