The radius of the circle is increasing uniformly at the rate of 3 cm per second. Find the rate at which the area of the circle is increasing when the radius is 10 cm.

Leave cm alone the range of the circle at time

Pace of increment of span of circle = 3 cm/sec

dx/dt is positive and = 3 cm/sec

Let y be the space of the circle.

Pace of progress of space of circle =

=

= 

Putting = 10 cm (given),dy/dt

= cm2/sec

Since dy/dt  is positive, along these lines surface region is expanding at the pace of cm2/sec.