a.
The volume of the box V = 4x³ - 72x² + 324x
Since the dimensions of the square piece of paper are 18 inches each, and we cut out a length x from each side to give a total length of 2x cut from each side. So, each dimension is L = 18 - 2x.
Since the height of the open box is x and its base is a square, the volume of the open box ix V = L²x
= (18 - 2x)²x
= (324 - 72x + 4x²)x
= 324x - 72x² + 4x³
The volume of the box V = 4x³ - 72x² + 324x
b.
The minimum value of length of the sides of the squares cut from each corner is x = 3 inches.
- the length of the box, L = 12 inches,
- the width of the box = 12 inches
- and the height of the box, x = 3 inches.
Since the volume of the box is 432 cubic inches,
V = 324x - 72x² + 4x³
324x - 72x² + 4x³ = 432
4x³ - 72x² + 324x - 432 = 0
x³ - 18x² + 81x - 108 = 0
A factor of the expression is x - 3
So, x³ - 18x² + 81x - 108 ÷ x - 3 = x² - 15x + 36
So, x³ - 18x² + 81x - 108 = (x² - 15x + 36)(x - 3) = 0
Factorizing the expression x² - 15x + 36 = 0
x² - 3x - 12x + 36 = 0
x(x - 3) - 12(x - 3) = 0
(x - 3)(x - 12) = 0
So, x³ - 18x² + 81x - 108 = (x - 3)(x - 3)(x - 12) = 0
So, (x - 3)²(x - 12) = 0
(x - 3)² = 0 and (x - 12) = 0
x - 3 = √0 and x - 12 = 0
x - 3 = 0 and x - 12 = 0
x = 3 twice and x = 12
Since x = 3 is the minimum value, the minimum value of x = 3.
Since the length of the box, L = 18 - 2x
= 18 - 2(3)
= 18 - 6
= 12 inches
The width of the box = L = 12 inches
The height of the box = x = 3 inches.
So,
The minimum value of length of the sides of the squares cut from each corner is x = 3 inches.
- the length of the box, L = 12 inches,
- the width of the box = 12 inches
- and the height of the box, x = 3 inches.
Learn more about volume of a box here:
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