Mathematics

Mathematics

Problem

A 60 cm60\text{ cm} by 30 cm30\text{ cm} rectangular sheet of metal will be made into an open-top box by cutting identical squares of side length xx centimeters from each corner and folding up the sides. Determine the value of xx (to two decimal places) that maximizes the volume of the box.
Intuitive explanation

When you cut squares from the corners and fold up, you're trading away corner material to create height—the key is that the base shrinks while the box gets taller. The volume function V(x)=x(60−2x)(30−2x)V(x) = x(60-2x)(30-2x) captures this trade-off: xx is your height, and (60−2x)(60-2x) and (30−2x)(30-2x) are the resulting base dimensions. To maximize, find where dVdx=0\frac{dV}{dx} = 0, then verify it's a maximum by checking the second derivative or the domain constraint (x<15x < 15).

Intuitive explanation

When you cut squares from the corners and fold up, you're trading away corner material to create height—the key is that the base shrinks while the box gets taller. The volume function V(x)=x(60−2x)(30−2x)V(x) = x(60-2x)(30-2x) captures this trade-off: xx is your height, and (60−2x)(60-2x) and (30−2x)(30-2x) are the resulting base dimensions. To maximize, find where dVdx=0\frac{dV}{dx} = 0, then verify it's a maximum by checking the second derivative or the domain constraint (x<15x < 15).

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