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Holt CA Course 1 10-4 Area of Triangles and Trapezoids AF3.1 Use variables in expressions describing geometric quantities (e.g., P = 2w + 2l, A = bh, C = d – the formulas for the perimeter of a rectangle, the area of a triangle, and the circumference of a circle, respectively). Also covered: AF1.2, AF3.2 California Standards 1212

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Holt CA Course 1 10-4 Area of Triangles and Trapezoids

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Holt CA Course 1 10-4 Area of Triangles and Trapezoids A. Find the area of the triangle. Additional Example 1: Finding the Area of a Triangle 5 8 A = 1212 bh Use the formula. A = 1212 (8 · 5) Substitute 8 for b and 5 for h. A = 20 The area of the triangle is 20 square units.

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Holt CA Course 1 10-4 Area of Triangles and Trapezoids B. Find the area of the triangle. Additional Example 1: Finding the Area of a Triangle 9 A = 1212 bh Use the formula. A = 1212 (12 · 9) Substitute 12 for b and 9 for h. A = 54 The area of the triangle is 54 square units. 12

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Holt CA Course 1 10-4 Area of Triangles and Trapezoids A. Find the area of the triangle. A = 1212 bh Use the formula. A = 1212 (6 · 9) Substitute 6 for b and 9 for h. A = 27 The area of the triangle is 27 square units. Check It Out! Example 1 6 9

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Holt CA Course 1 10-4 Area of Triangles and Trapezoids B. Find the area of the triangle. A = 1212 bh Use the formula. A = 1212 (7 · 10) Substitute 7 for b and 10 for h. A = 35 The area of the triangle is 35 square units. Check It Out! Example 1 10 7

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Holt CA Course 1 10-4 Area of Triangles and Trapezoids The two parallel sides of a trapezoid are its bases, b 1 and b 2. The height of a trapezoid is the perpendicular distance between the bases. h b1b1 b2b2

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Holt CA Course 1 10-4 Area of Triangles and Trapezoids In the term b 1, the number 1 is called a subscript. It is read as “b-one” or “b sub-one.” Reading Math

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Holt CA Course 1 10-4 Area of Triangles and Trapezoids A. Find the area of the trapezoid. Additional Example 2: Finding the Area of a Trapezoid 5 in. 6 in. 9 in. A = 1212 h(b 1 + b 2 ) Use the formula. A = 1212 · 6(9 + 5) A = 1212 · 6(14) A = 42 The area of the trapezoid is 42 in 2. Substitute. Multiply. Add.

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Holt CA Course 1 10-4 Area of Triangles and Trapezoids B. Find the area of the trapezoid. Additional Example 2: Finding the Area of a Trapezoid A = 1212 h(b 1 + b 2 ) Use the formula. A = 1212 · 7(16 + 12) A = 1212 · 7(28) A = 98 The area of the trapezoid is 98 cm 2. Substitute. Multiply. Add. 12 cm 16 cm 7 cm

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Holt CA Course 1 10-4 Area of Triangles and Trapezoids A. Find the area of the trapezoid. A = 1212 h(b 1 + b 2 ) Use the formula. A = 1212 · 6(11 + 4) A = 1212 · 6(15) A = 45 The area of the trapezoid is 45 in 2. Substitute. Multiply. Add. Check It Out! Example 2 4 in. 6 in. 11 in.

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Holt CA Course 1 10-4 Area of Triangles and Trapezoids B. Find the area of the trapezoid. A = 1212 h(b 1 + b 2 ) Use the formula. A = 1212 · 9(5 + 16) A = 1212 · 9(21) A = 94.5 The area of the trapezoid is 94.5 cm 2. Substitute. Multiply. Add. Check It Out! Example 2 16 cm 5 cm 9 cm

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Holt CA Course 1 10-4 Area of Triangles and Trapezoids The state of Wisconsin is shaped somewhat like a trapezoid. What is the approximate area of the state? Additional Example 3: Geometry Application A = 1212 h(b 1 + b 2 ) Use the formula. A = 1212 · 300(153 + 220) A = 1212 · 300(373) A = 55,950 The area of Wisconsin is approximately 56,000 square miles. Substitute. Multiply. Add.

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Holt CA Course 1 10-4 Area of Triangles and Trapezoids A large preserve has a similar trapezoid shape. What is the approximate area of the preserve? Check It Out! Example 3 232 mi 116 mi A = 1212 h(b 1 + b 2 ) Use the formula. A = 1212 · 129(232 + 116) A = 1212 · 129(348) A = 22,446 The area of the preserve is approximately 22,446 square miles. Substitute. Multiply. Add. 129 mi

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