Question

Find how fast (a) the circumference (b)the area, if a cicle increases when the radius increases.

Answer 1

For absolute change rates:
dC/dt = 2*pi*dR/dt

dA/dt = 2*pi*R*dR/dt

For relative change rates
(1/C)dC/dt = (1/R) dR/dt

(1/A) dA/dt = (2/R)*dR/dt