Answer:
Hence the width, length is 20 cm and height is 10 cm
Step-by-step explanation:
Since the box has a square base, let length = width = x. Also, let the height = y, therefore:
The volume of box = width * length * height
4000 = x * x * y
4000 = x²y
y=4000/x²
The surface area (SA) = area of the base + sum of the area of each side
SA = x² + xy + xy + xy + xy
SA = x² + 4xy
substitute y = 4000/x²
SA = x² + 4x(4000/x²)
SA = x² + 16000/x
Taking the derivative:
SA' = 2x - 16000/x²
making SA' = 0:
0 = 2x - 16000/x²
2x = 16000/x²
2x³ = 16000
x³ = 8000
x = 20 cm
y = 4000 / x² = 4000 / 20² = 10 cm
Hence the width, length is 20 cm and height is 10 cm
