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Suppose the length and width of the box in exercise 12 double. Does the surface area S double? Explain

10cm 24cm and 27cm are the lengths in exercise 12

User Mrog
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1 Answer

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No, it does not.

In general, surface area is the sum of the areas of each face of a prism. In a rectangular prism, we have length, width, and height.

The area of the bottom of the prism and the top of the prism is the same, and can be represented as l*w. This means that together, it is 2lw.

The area of the left and right faces of the prism is the same, and can be represented as l*h. This means that together, it is 2lh.

The area of the front and back faces of the prism is the same, and can be represented as w*h. This means that together, it is 2wh.

This gives us the equation

SA = 2lw+2lh+2wh

If we double the length and width, making them each 2l, we then have:

SA = 2(2l*2w) + 2(2l*h) + 2(2w*h)
= 2(4lw) + 4lh + 4wh
= 8lw + 4lh + 4wh

If the surface area had been doubled, we would expect
4lw + 4lh + 4wh

No, it is not doubled.
User Amitabha Roy
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