Question

Find the dimensions of the rectangular box of maximum volume if the sum of the length, width, and height equals 180. (Give exact answers. Use symbolic notation and fractions where needed.)

Answer 1

Step-by-step explanation:

Let the dimension of the box be x, y and z.

Volume of the box V = xyz

Since the box is a rectangular box, the base will be a square of equal length.

V = x²h where h is the height of the box

If the sum of the length, width, and height equals 180, then x+x+h = 180

2x+h = 180

h = 180-2x

Substitute h = 180-2x into the volume of the box

V = x²(180-2x)

V = 180x²-2x³

The box has its maximum volume when $\frac{dV}{dx} = 0$

$\frac{dV}{dx} = 360x-6x^{2}$

$360x-6x^{2} = 0\\360x = 6x^2\\360 = 6x\\6x = 360\\x = \frac{360}{6}\\ x = 60$

Since 2x+h = 180

Substitute x = 60 into the equation ang get the height h

2(60)+h = 180

120+h = 180

h = 180-120

h = 60

Hence the dimension of the rectangular box is 60 by 60 by 60