# Thread: Volume of a cube is changing...Differentiation

1. ## Volume of a cube is changing...Differentiation

The volume of a cube is changing at a rate of 18 cubic cm/second. How fast is the edge of the cube expanding when each edge is a)2cm and b)3cm.

Any help appreciated.Thanks

2. Let x = length of the side of the cube.

Volume of a cube is $v(x)=x^3$, therefore $dv/dx = 3x^2$. Therefore when $x = 2$, $dv/dx = 12$, and when $x = 3$, $dv/dx = 27$.