A circle is being formed with a piece of wire which is 40cm long. When the wire is heated, the curcumference of the circle increases at the rate of 2/5 cm s^-1. Find (in the terms of pi) the rate of change of the radius of the circle
Circumference = 2*pi*r
Differentiating this with respect to time, we have
dC / dt = 2*pi *dr / dt
2.5 cm/s = 2*pi * dr/dt divide both sides by 2*pi
[ 2.5 ]/ [2 *pi] cm/s = dr/dt = [ 5 / (4pi) ] cm/s
