The volume of a cube is increasing at the rate of 8 cm3/s. How fast is the surface area increasing when the length of an edge is 12 cm?


Let a be the length of a side, V be the volume and S be the surface area of the cube.

Then, V = a3 and S = 6a2 where a is the function of time t.


Now, It is given that


Then, by using the chain rule, we get,



………………(1)



So, when a = 12cm, then,


Therefore, if the length of the edge of the cube is 12cm, then the surface area is increasing at the rate of .


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