The length x of a rectangle is decreasing at the rate of 5 cm`//`minute and the width y is increasing at the rate of 4 cm`//`minute.When x=8cm and y=6cm, find the rates of change of the perimeter.

Explanation

Here, dx/dt=5 cm`//`minute and dy/dt=4cm`//`minute, where t be the time.
Perimeter of the rectangle, P=2(x+y).
`therefore`rate of change of perimeter, `(dP)/dt=2(dx/dt+dy/dt)=2(4+5)=18` cm `//`minute.