Applications of derevatives

Question

The length x of rectangle is decreasing at the rate of 5cm/minute and the width y is increasing at the rate of 5cm /minute.When x= 8cm and y= 6cm ,find the rates of change of (i) Perimeter,and (ii)the area of the rectangle.

Answer 1

x = 8, y = 6, dx/dt = -5 and dy/dt = 5

P = 2x + 2y

dP/dt = 2x(dx/dt) + 2y(dy/dt)

A = xy

dA/dt = x(dy/dt) + y(dx/dt)