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Math Help - Volume of a cube is changing...Differentiation

  1. #1
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    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
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  2. #2
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    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.
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