The radius of a spherical ballon, of 30units , increases at the rate of 2units per second. then it's curved surface area increase by?
the answer is given as 480pie sq units/sec.
but for spheres
for r=30, CSA= 3600pie sq units.
after 1sec,
for r=32, CSA = 4096pie sq units.
so, change in CSA = 496pie sq units/sec. why is this wrong?