Question

If 1,200 cm2 of material is available to make a box with a square base and an open top, find the maximum volume of the box in cubic cm. For example, if the answer is 2,000 cm3 write 2000.

Answer 1

4000cm³

Explanation:

Volume of the rectangular box = x²h

Surface area S = x²+4xh

x is the side length of the square base

h is the height

Given

Surface area = 1200cm²

Substitute into the formula S = x²+4xh

1200 = x²+4xh

From V = x²h

h= V/x²

1200 = x² + 4x (V/x² )

1200 = x² + 4V/x

1200x = x³ + 4V

1200x - x³ = 4V

V = 1200x/4- x³/4

V = 300x - x³/4

To maximize the volume, dV/dx = 0

dV/dx = 300 -3x²/4

0 = 300 -3x²/4

0 = 1200 - 3x²

3x² = 1200

x² = 400

x = 20cm

Since 1200 = x²+4xh

1200 = 400+80h

80h = 1200-400

80h = 800

h = 10cm

Find the volume;

Volume = 400 * 10 Volume -= 4000

Hence the maximum volume of the box in cubic cm is 4000 cm³