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If the total cost function is given by C(x)=x33−2x2+9x−70C(x)=\frac{x^3}{3}-2x^2+9x-70 and the selling price per unit is ₹6, then for what value of xx will the profit be maximum?

Solution

✅ Correct Option: 3

Profit P=6x−C(x)=−x33+2x2−3x+70P=6x-C(x)=-\frac{x^3}{3}+2x^2-3x+70. Then P′=−x2+4x−3=−(x−1)(x−3)P'=-x^2+4x-3=-(x-1)(x-3), zero at x=1,3x=1,3. Since P′′=−2x+4P''=-2x+4 is negative at x=3x=3, profit is maximum at x=3x=3.

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