Me answer this. riddle: i am the most basic building block in geometry. i look like a dot but you actually can't see me, unless you "see" me in your mind. although i am nothing, 2 of me makes a 1-dimensional being and 3 of me, not on the same line, make a 2-dimensional being! what am i?

Suppose that the price p (in dollars) and the weekly sales x (in thousands of units) of a certain commodity satisfy the demand equation 4p cubedplusx squaredequals38 comma 400. determine the rate at which sales are changing at a time when xequals80, pequals20, and the price is falling at the rate of $.20 per week.