1.

The edge of a cube is increasing at a rate of 7 cm/s. Find the rate of change of area of the cube when x=6 cm.(a) 578 cm^2/s(b) 498 cm^2/s(c) 504 cm^2/s(d) 688 cm^2/sI had been asked this question in unit test.The doubt is from Derivatives Application topic in portion Application of Derivatives of Mathematics – Class 12

Answer» CORRECT option is (c) 504 cm^2/s

The EXPLANATION: Let the edge of the cube be x. The rate of change of edge of the cube is given by \(\frac{dx}{dt}\)=7cm/s.

The AREA of the cube is A=6x^2

∴\(\frac{dA}{dt}=\frac{d}{dt} \)(6x^2)=12X.\(\frac{dx}{dt}\)=12x×7=84x

\(\frac{dA}{dt}\)|_x=6=84×6=504 cm^2/s.


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