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Calculate Triangle Areas

Learn how to find the area of a triangle using base and height measurements. Practice with examples and solve multiple-choice questions.

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Calculate Triangle Areas

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  1. Transparency 2 Click the mouse button or press the Space Bar to display the answers.

  2. Example 2-1a Objective Find the areas of triangles

  3. Example 2-1a Vocabulary Triangle A polygon with 3 sides

  4. Lesson 2 Contents Example 1Find the Area of a Triangle Example 2Find the Area of a Triangle Example 3Use Area to Solve a Problem

  5. Example 2-1a Find the area of the triangle.  5 units 2 3 4 5 Base 1 Write formula for area of a triangle Count number of units of the length of a base Replace b with 5 units 1/2

  6. Example 2-1a 1 Find the area of the triangle. 2 3 Height 4 5 6  5 units  8 units 7 8 Count number of units of the height Replace h with 8 units 1/2

  7. Example 2-1a Find the area of the triangle. Multiply the numbers  5  8  5 units  8 units Multiply the units unit  unit Answer: unit2 A = 20 1/2

  8. Example 2-1b Find the area of the triangle. Answer: 9 units2 1/2

  9. Example 2-2a Find the area of the triangle. Round to the nearest hundredth  16.4 cm  7.9 cm Write formula for area of a triangle Replace b with 16.4 cm Remember: The base is opposite the vertex Replace h with 7.9 cm 2/2

  10. Example 2-2a Multiply the numbers  16.4  7.9 Find the area of the triangle. Round to the nearest hundredth Since the dimensions are decimals the answer must be decimals  16.4 cm  7.9 cm Multiply the units cm  cm Answer: A = 64.78 cm2 2/2

  11. Example 2-2b Find the area of the triangle. Round to the nearest hundredth Answer: 12.18 in2 2/2

  12. End of Lesson 2 Assignment

  13. MULTIPLE-CHOICE TEST ITEM Which ratio compares the area of the shaded triangle to the area of the large square? A 1 to 2 B 1 to 4 C 1 to 8 D 1 to 16 Example 2-3a 3/3

  14. Example 2-3a Read the Test Item You need to find the ratio that compares the area of the shaded triangle to the area of the large square. Solve the Test Item First find the area of the triangle and the area of the square. Area of Triangle Area of Square 3/3

  15. Since , the ratio is 2 to 16, or 1 to 8 in simplest form. Example 2-3a Now find the ratio. Answer: C 3/3

  16. MULTIPLE-CHOICE TEST ITEM Which ratio compares the area of the shaded triangle to the area of the large square? A 1 to 2 B 1 to 4 C 1 to 8 D 1 to 16 Example 2-3b Answer: B

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