Suppose that the demand function for a product takes the form Qd = (A - BP)D where

Question:

Suppose that the demand function for a product takes the form Qd = (A - BP)D where A, B, and Dare positive numbers. Derive a formula for the elasticity of demand as a function of the price. (Your formula can have A, B, and Din it.) At what price is consumers' total expenditure the largest?