Both the problem and my attempt at a solution are provided. However, I become stuck. The answer book (question 27, as pictured in the next post, the upload size limit made me create a second post and both images are about 4mb), suggests that I use dV/dH, which is the portion of the cone volume formula: pih^2/4 (once the square is distributed to the radius). I am having trouble understanding why this part of the formula is considered to be dV/dH, and I am not especially strong in Leibniz notation; I prefer to use prime notation. I suppose that weakness is catching up with me on this problem. Thank you in advance for any replies.