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Tamil Nadu Board of Secondary EducationHSC Commerce Class 11

The total cost function y for x units is given by y = 4x(x+2x+1)+6. Prove that marginal cost [MC] decreases as x increases. - Business Mathematics and Statistics

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Question

The total cost function y for x units is given by y = `4x((x+2)/(x+1)) + 6`. Prove that marginal cost [MC] decreases as x increases.

Sum
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Solution

Given y = `4x((x+2)/(x+1)) + 6`

y = `(4x^2 + 8x)/(x + 1) + 6`

Differentiating with respect to 'x' we get,

Marginal cost = `"dy"/"dx" = ((x+1)(8x+8)-(4x^2 + 8x)(1))/(x + 1)^2`

`= (8x^2 + 8x + 8x + 8 - 4x^2 - 8x)/(x + 1)^2`

`= (4x^2 + 8x + 8)/(x + 1)^2`

`= (4(x^2 + 2x + 2))/(x + 1)^2`

`= (4(x^2 + 2x + 1 + 1))/(x + 1)^2`

`= 4 ((x + 1)^2/(x + 1)^2 + 1/(x + 1)^2)`

Marginal Cost = `4(1 + 1/(1 + x)^2)`

Since `1/(1 + x)^2` is in the denominator, as x increases marginal cost decreases.

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Chapter 6: Applications of Differentiation - Miscellaneous Problems [Page 156]

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Samacheer Kalvi Business Mathematics and Statistics [English] Class 11 TN Board
Chapter 6 Applications of Differentiation
Miscellaneous Problems | Q 5 | Page 156

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