SOLUTION: Hai sir, please help me on this problem, " "The volume of a cube is increasing at a rate of 9 cubic centimeters per second. How fast is the surface area increasing when the leng

Algebra ->  Testmodule -> SOLUTION: Hai sir, please help me on this problem, " "The volume of a cube is increasing at a rate of 9 cubic centimeters per second. How fast is the surface area increasing when the leng      Log On


   

Question 397768: Hai sir, please help me on this problem,
"
"The volume of a cube is increasing at a rate of 9 cubic centimeters per second. How fast is the surface area increasing when the length of an edge is 4 centimeters?
a)9 cm2/s
b)8 cm2/s
c)6 cm2/s
d)None of these
Answer by robertb(5830) About Me  (Show Source):
You can put this solution on YOUR website!
Volume of cube is V+=+e%5E3 ==> dV%2Fdt+=+3e%5E2%28+de%2Fdt%29
==> 9+=+3%2A4%5E2%2A%28+de%2Fdt%29 <==> de%2Fdt+=+3%2F16 when e = 4 cm.
Now the surface area S+=+6e%5E2 ==> dS%2Fdt+=+12e%28de%2Fdt%29+=+12%2A4%2A%283%2F16%29+=+9sq. cm. per second.
Therefore the answer is a.