CBSE Class 12-science Answered

Based upon the information given in the question, you should be able to reduce your equation ultimately into a single variable equation. I used to write my equation in terms of the variable which we need to find out in the question. So, if the question is asking to find the radius of a cylinder or cone, I would write height also in terms of radius and get my final equation in terms of radius (using similarlity or trignometry) and then differentiate it with respect to radius. 

 

However, if differentiation wrt to radius is really complex, I might do it the other way i.e. write equation in terms of height and then differentiate it wrt to height to find the height and then the corresponding radius.