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The cost function of a product is given by C(x)=13x3−45x2−900x+36C(x)=\frac{1}{3}x^3-45x^2-900x+36, where x is the number of units produced. In order to minimize the marginal cost, how many units of the product must be produced?

Solution

✅ Correct Option: 4

Marginal cost is MC=C′(x)=x2−90x−900MC=C'(x)=x^2-90x-900.

To minimise it, set d(MC)dx=2x−90=0\frac{d(MC)}{dx}=2x-90=0, giving x=45x=45.

Since d2(MC)dx2=2>0\frac{d^2(MC)}{dx^2}=2>0, this is indeed a minimum.

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