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The total cost of manufacturing x articles is C = 47x + 300x2 - x4. Find x, for which average cost is increasing

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प्रश्न

The total cost of manufacturing x articles is C = 47x + 300x2 − x4.  Find x, for which average cost is increasing.

योग
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उत्तर

Given,
Total cost function is (C) = 47x + 300x2 – x4 
Average cost CA = `"C"/"A"`

∴ CA = `(47 x + 300x^2 – x^4)/x`

∴ CA = `(x(47 + 300x – x^3))/x`

∴ CA = 47 + 300x – x3

`"dC"_"A"/"dx" = "d"/"dx" 47 + 300x  –  x^3`

∴ `"dC"_"A"/"dx"` = 0 + 300 – 3x2

∴ `"dC"_"A"/"dx"` = 3(100 –  x2)

Since average cost, CA is an increasing function, `"dC"_"A"/"dx" > 0`

∴ 3(100 – x2) > 0

∴ 100 – x2 > 0

∴ 100 > x2

∴ x2 < 100

∴ – 10 < x < 10

∴ x > – 10 and x < 10

But x > – 10 is not possible.     ...[∵ x > 0]

∴ x < 10  

∴ The average cost CA is increasing for x < 10. 

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अध्याय 4: Applications of Derivatives - Exercise 4.4 [पृष्ठ ११२]

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