Two positive numbers whose sum is 60 and the product of the square of one number and other number is maximum are : |
45 and 15 30 and 30 50 and 10 20 and 40 |
20 and 40 |
Let the two positive numbers be $x$ and $y$, with $x + y = 60$. Let the function to maximize be $P = x^2 y$. Express $y$ in terms of $x$: $y = 60 - x$. Then, $P = x^2 (60 - x) = 60x^2 - x^3$ Differentiating $P$ with respect to $x$: $\frac{dP}{dx} = 120x - 3x^2$ Set $\frac{dP}{dx} = 0$: $120x - 3x^2 = 0$ $x(120 - 3x) = 0$ $x = 0$ or $x = 40$ Since numbers are positive, $x = 40$ Then $y = 60 - 40 = 20$ Therefore, the two numbers are $40$ and $20$. |