This problem deals the rate of change.
For the formula of the area of a circle, we differentiate both sides with respect to time t.
(A = πr^2) d/dt
dA/dt = 2πr (dr/dt)
Since we don't know yet the radius r, the area of a circle is given.
A = πr^2
r^2 = A/π = 4π/π
r^2 = 4
r = 2 cm
Therefore, the rate of the radius is
dA/dt = 2πr (dr/dt)
dr/dt = (dA/dt)/(2πr)
dr/dt = π/(2π*2)
dr/dt = 0.25 cm/min
Hope this helps.
