Q.The profit of a function $p(x)$ is maximum when :

Profit peaks when $MC = MR$, i.e. $MC - MR = 0$.

Profit is total revenue minus total cost: $p(x) = R(x) - C(x)$. For a maximum, differentiate and set the derivative to zero:

$\frac{dp}{dx} = \frac{dR}{dx} - \frac{dC}{dx} = MR - MC = 0.$

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