Final answer:
To find the maximum volume of the box, we can use calculus to determine the value of x that maximizes the volume function. By taking the derivative of the volume function and setting it equal to zero, we can solve for x. The only valid solution is x = 6 inches.
Step-by-step explanation:
To find the dimensions of the square to be cut out, we need to maximize the volume of the box. Let's assume the length of each side of the small square to be x inches.
When the flaps are folded up, the length of the box would be (42 - 2x) inches, and the width would be (36 - 2x) inches. The height of the box would be x inches. The volume of the box is given by V = length x width x height.
V = (42 - 2x)(36 - 2x)(x) = 4x³ - 156x² + 1512x.
To find the maximum volume, we need to find the value of x that maximizes the function V. We can do this by taking the derivative of V and setting it equal to zero: dV/dx = 12x² - 312x + 1512 = 0.
Solving this equation gives us x = 6 or x = 18. Since x must be less than half the length of the side of the plastic sheet (which is 36 inches), the only valid solution is x = 6 inches.
Therefore, the length of the side of the square to be cut out from each corner should be 6 inches.