13. The area of a sector in a circle is given by the formula A = trae where r is the radius and o is the central angle measured in radians. (a) Find the rate of change of A with respect to 8 if r remains constant. (b) Find the rate of change of A with respect for if & remains constant (c) Find the rate of change of o with respect tor if d remains constant. 14. The total surface area of a right circular cylinder is given by the formula A = 2ar(r + A) where r is the radius and h is the height. (a) Find the rate of change of A with respect to A if rremains constant. (b) Find the rate of change of / with respect to rif remains constant