**Area of Squares, Rectangles, and Triangles**

The **area** of a geometric figure is the number of square units contained in its surface. For example, the area of the 3-inch by 2-inch rectangle is 6 square inches as shown in Fig. 9-7 .

Area is measured in square units. A square inch is a square whose sides measure one inch. A square foot is a square whose sides measure one foot, etc. Square units are abbreviated using two for the exponent:

- 1 square inch = 1 in.
^{2} - 1 square foot = 1 ft
^{2} - 1 square yard = 1 yd
^{2} - 1 square mile = 1 mi
^{2}

**Area of a Rectangle**

*The area of a rectangle is found by using the formula A = lw, where l is the length and w is the width*.

**Example 1**

Find the area of the rectangle shown in Fig. 9-8 .

**Solution 1**

**Area of a Square**

*The area of a square can be found by using the formula A = s ^{2}, where s is the length of its side*.

**Example 2**

Find the area of the square shown in Fig. 9-9 .

**Solution 2**

**Area of a Triangle**

To find the area of a triangle you need to know the measure of its *altitude*. The **altitude** of a triangle is the measure of a perpendicular line from its highest point to its base (the side opposite its highest point). See Fig. 9-10.

*The area of a triangle can be found by using the formula * , where b is the base and h is the height or altitude .

**Example 3**

Find the area of the triangle shown in Fig. 9-11 .

**Solution 3**

**Area of Squares, Rectangles, and Triangles Practice Problems**

**Practice**

1. Find the area of a rectangle whose length is 123 yards and whose width is 53 yards.

2. Find the area of a square whose side is 53 inches.

3. Find the area of a triangle whose base is 16 inches and whose height is 9 inches.

**Answers**

1. 6519 yd ^{2}

2. 2809 in. ^{2}

3. 72 in. ^{2}

Practice problems for these concepts can be found at: Informal Geometry Practice Test.

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