Question

THE EDGES OF A CUBE ARE EXPANDING A A RATE OF 5 CENTIMETERS PER SECOND.HOW FAST IS THE SURFACE AREA CHANGING WHEN EACH EGDE IS 4.5 CENTIMETERS??

Answer 1

A=6xr^2
dA/dt=6xd(r^2)/dt=6x2rxdr/dt=12rxdr/dt
at r=4.5 and dr/dt=5
dA/dt=12x4.5x5=270 cm^2/sec