Posted by Minx on Wednesday, August 17, 2011 at 10:28pm.
a cube is expanding and its volume is increasing at the rate 96 cubic centimetres/second when the side is 4 cm.Find the rate at which the:
a.side is increasing when the side is 4 cm
b.surface area is increasing when the side is 4cm
V= x^3 A= 6x^2

math  Reiny, Wednesday, August 17, 2011 at 10:59pm
dV/dt = 3x^2 dx/dt
96 = 3(4^2)dx/dt
dx/dt = 96/48 = 2 cm/second
A = 6x^2
dA/dt = 12x dx/dt
dA/dt = 12(4)(2) = 96 cm^2/sec 
math  Minx, Wednesday, August 17, 2011 at 11:06pm
A spherical balloon is being inflated and its radius is changing at the rate of 2m/minute. When the radius is 4m, find the rate at which the:
(a).volume is increasing
V= 3/4 pie r^2
(b). surface area is increasing
A = 4 pie r^2