You are planning to make an open rectangular box from a 25​-in.-by-49​-in. piece of cardboard by cutting congruent squares from the corners and folding up the sides. What are the dimensions of the box of largest volume you can make this​ way, and what is its​ volume?

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Answer:

The dimensions of the box are 38.48 x 14.48 x 5.26 in.

Step-by-step explanation:

We will have a piece of cardboard with squares of side x cut from the corners to make a open box.

The volume of the box can be written as:

[tex]V=A\cdot B\cdot x\\\\V=(49-2x)\cdot (25-2x)\cdot x\\\\V=x\cdot (4x^2-2x*(49+25)+49*25)\\\\V=4x^3-148x^2+1225x[/tex]

To calculate the maximum volume, we derive and equal to zero

[tex]dV/dx=12x^2-296x+1225=0[/tex]

We apply the quadratic equation to know the roots of the equation

[tex]x=\frac{-b\pm\sqrt{b^24ac}}{2a}\\\\x=\frac{296\pm\sqrt{296^2-4*12*1225}}{2*12} =\frac{296\pm\sqrt{87616-58800}}{24}= \frac{296\pm\sqrt{28816}}{24}\\\\x=\frac{296\pm169.75}{24}= 12.333\pm7.073\\\\\\x_1=12.333+7.073=19.406\\\\x_2=12.333-7.073=5.26[/tex]

The first solution is physically impossible, as the side that is cut would be bigger than 25.

So the real solution is for x=5.26 in.

Then, the dimensions of the box are:

[tex]A=49-2x=49-2*5.26=49-10.52=38.48\\\\B=25-2x=25-10.52=14.48[/tex]

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The dimensions of the box of largest volume you can make with the given cardboard is;

Length = 38.48 in

Width = 14.48 in

Height = 5.26 in

We are given the dimensions of the cardboard as; 25​-in. by 49​-in.

Let us denote the box as follows;

Length = l

Width = w

Height = h

If we cut congruent squares from the corners, it means that if the length of each square cut is x, then the new dimensions are;

Length = 49 - 2x

Width = 25 - 2x

Height = x

Formula for volume of a box is;

V = Length × width × height

V = (49 - 2x) × (25 - 2x) × (x)

V = 4x³ - 148x² + 1225x

Now, the largest volume will happen at the dimensions when dV/dx = 0.

dV/dx = 12x² - 256x + 1225

At dV/dx = 0;

12x² - 256x + 1225 = 0

Using online quadratic equation solver, we have;

x = 5.26 or 19.406

We will take 5.26 in instead of 19.406 because 19.406 would mean that the length cut out would be longer than 25 in.

Thus, putting x = 5.26 into the dimensions expression gives;

Length = 49 - 2(5.26) = 38.48 in

Width = 25 - 2(5.26) = 14.48 in

Height = 5.26 in

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