Big Ideas Math: Modeling Real Life, Grade 8
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Big Ideas Math: Modeling Real Life, Grade 8 View details
2. The Pythagorean Theorem
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Exercise 33 Page 388

When converting from centimeters to inches, remember that 1 inch is 2.54 centimeters.

No, see solution.

Practice makes perfect
We want to know if we can fit a cylindrical rod with a length of 342.9 centimeters in a box that has a length of 30 inches, a width of 40 inches, and a height of 120 inches. To compare the dimensions of the box and the length of the rod, they should have the same units. Let's start by converting 342.9 centimeters to inches using the conversion factor 1in2.54cm. 342.9cm* 1in2.54cm Now, we can evaluate the expression for the length of the rod.
342.9cm* 1in/2.54cm
342.9 cm* 1in/2.54 cm
342.9* 1in/2.54
â–Ľ
Simplify
342.9* 1/2.54in
342.9/2.54in
135in
The length of the cylindrical rod is 135 inches. Let's draw the box and the rod.
A box in the shape of rectangular right prism with the width of 30 inches, length of 40 inches and the height of 120 inches and a right cylinder with the height if 135 inches
Notice that the length of the rod, 135 inches, is longer than the longest side of the box, 120 inches. This means that the rod cannot fit in the box standing up. But we can also check if the rod will fit in the box diagonally. We can do this in three steps.
  1. Find the diagonal of the base of the box.
  2. Find the diagonal of the box.
  3. Compare the length of the diagonal of the box and the length of the rod.

We will do it one step at a time.

Diagonal of the Base of the Box

Let's start by drawing the diagonal of the base of the box.

base of the box with diagonal of the base marked

We can see that the diagonal divides the base of the box into two right triangles, with the diagonal as the hypotenuse. This means that we can use the Pythagorean Theorem to find the length of the diagonal of the base. a^2+b^2=c^2 In the formula, a and b are the legs and c is the hypotenuse of a right triangle. Let's identify a, b, and c on the diagram.

sides of the triangle marked
We have that a= 30 inches and b= 40 inches. Let's substitute these values into the formula!
a^2+b^2=c^2
30^2+ 40^2=c^2
â–Ľ
Solve for c
900+1600=c^2
2500=c^2
c^2=2500
sqrt(c^2)=sqrt(2500)
c=sqrt(2500)
c=50
The diagonal of the base of the box is 50 inches long.

Diagonal of the Box

We know that the diagonal of the base of the box, the diagonal of the box, and the height of the triangle create a right triangle. Let's add this information to the diagram.

triangle with the diagonal of the box as the hypotenuse

The diagonal of the box is the hypotenuse of the triangle. This means that we can once again use the Pythagorean Theorem to find the length. Let's identify the legs a and b, and the hypotenuse c on the diagram.

triangle with the diagonal of the box as the hypotenuse and its sides marked
This time a is 50 inches and b is 120 inches. Let's substitute these values into the formula.
a^2+b^2=c^2
50^2+ 120^2=c^2
â–Ľ
Solve for c
2500+14 400=c^2
16 900=c^2
c^2=16 900
sqrt(c^2)=sqrt(16 900)
c=sqrt(16 900)
c=130
The diagonal of the box from a top corner to the opposite bottom corner is 130 inches long.

Compare the Length of the Diagonal of the Box and the Length of the Rod

Finally, we can compare the length of the diagonal of the box and the length of the rod. Let's do it! 130 < 135 The diagonal of the box is not as long as the length of the rod. This means that the rod will not fit in the box.