Big Ideas Math: Modeling Real Life, Grade 8
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6. Similar Figures
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Exercise 5 Page 80

Two figures are similar if the corresponding sides are proportional.

No, see solution.

Practice makes perfect

We know that a medical supplier sells gauze in large and small rectangular sheets. Consider the given information about each type of sheet.

  • A large sheet has a length of 9 inches and an area of 45 square inches.
  • A small sheet has a length of 4 inches and a width of 3 inches.
We want to know if the sheets are similar. To do so, let's start by recalling the formula for the area of a rectangle. A= l * w Here, l indicates the length of the rectangle and w the width. Let's start by finding the width of the larger sheet. We will substitute l= 9 and A= 45 into the formula for the area and solve for w.
A= l * w
â–Ľ
Solve for w
45 = 9 * w
45/9 =9 * w/9
45/9 =9 * w/9
45/9 =w
5=w
w=5
The width of the larger sheet is equal to 5 inches. Now that we have all the information about the side lengths of both sheets, we can use a condition for similarity to see if they are similar figures. To do so, we will write a proportion between the corresponding side lengths. l_1/l_2= w_1/w_2 Here, the subscript 1 represents the larger sheet and the subscript 2 represents the smaller sheet. This condition must be true if the sheets are similar. Let's substitute the known values into the equation to see if the sheets are similar. 9/4≠ 5/3 Therefore, the rectangular sheets are not similar because the corresponding sides lengths are not proportional.