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Area: Triangles and Trapezoids Lesson 10-2 p.509

Area: Triangles and Trapezoids Lesson 10-2 p.509. Start the Bellwork Quiz. Have your HW, red pen, and book on your desk. Triangles. When finding the area of triangles, remember that a triangle is half of a parallelogram. Triangles.

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Area: Triangles and Trapezoids Lesson 10-2 p.509

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  1. Area: Triangles and TrapezoidsLesson 10-2 p.509 Start the Bellwork Quiz. Have your HW, red pen, and book on your desk.

  2. Triangles • When finding the area of triangles, remember that a triangle is half of a parallelogram.

  3. Triangles • Now you can see why the formula for the area of a triangle makes sense: • A = bh or A = bh 2

  4. Triangles • Let’s look at an example: A = bh = 4 (5) = 20 2 2 2 or 10 ft2 5 feet 4 feet

  5. Try This • Find the areas: 7 miles 3 ft. 5 mi. 12 in. 6 miles

  6. Try This • Find the areas: 7 miles 3 ft. 5 mi. 12 in. 6 miles 216 in2 or 1.5 ft2

  7. Try This • Find the areas: 7 miles 3 ft. 5 mi. 12 in. 6 miles 216 in2 or 1.5 ft2 15 mi2

  8. Trapezoids • Trapezoids have different formula. It looks like this: • A = h (b1 + b2) or A = h(b1 + b2) 2 b1 h b2

  9. Trapezoids • A = h (b1 + b2) or A = h(b1 + b2) 2 Note that there are 2 bases—base 1 and base 2. The formula takes the average of the two bases multiplied by the height. b1 h b2

  10. Trapezoids • Let’s try an example: • A = h (b1 + b2) A = 3.5 (4 + 6) 2 2 A = 3.5 (5) = 17.5 ft2 4 ft 3.5 ft 6 feet

  11. Try This • Find the area: 24 mm 12 mm 33 mm

  12. Try This • Find the area: 24 mm 342 mm2 12 mm 33 mm

  13. Try This • Find the area: 4.5 feet 2 feet 4 feet

  14. Try This • Find the area: 4.5 feet 2 feet 13 ft2 4 feet

  15. Example • Some shapes look unusual, but when you remember just 3 formulas, you can calculate the area. Which two shapes do you see in the figure at the left?

  16. Example • There is a square (parallelogram) and a triangle. To find the area, first find the area of the parallelogram and then add it to the area of the triangle.

  17. Example The square has an area of A = bh or 3 (3) or 9 ft2. The triangle has an area of A = ½ bh or ½ (3) (2) or 3 ft2. The total area if 9 + 3 or 12 ft2 3 ft 2 ft

  18. Try This • Find the area: 6 cm 6 cm 4 cm 8 cm

  19. Try This • Here is a hint: 6 cm 6 cm 4 cm 8 cm

  20. Try This • Here is a hint: For the rectangle: A = bh A = 6 (4) = 24 cm2 For the trapezoid: A = ½ h (b1 + b2) A = ½ (2) (4 + 6) A = 10 cm2 Total area = 24 + 10 = 34 cm2 6 cm 6 cm 4 cm 8 cm

  21. Try This • Is there another way to divide this up? 6 cm 6 cm 4 cm 8 cm

  22. Try This • How about like this: 6 cm 6 cm 4 cm 8 cm

  23. Try This • How about like this: 6 cm For the rectangle: A = bh = 8 (4) = 32 cm2 For the triangle: A = ½ bh = ½ (2) (2) = 2 cm2 The total area is 32 + 2 or 34 cm2 6 cm 4 cm 8 cm

  24. Agenda • PA#38 • Pp.512-513 #8-16 even, 17, 19

  25. Please start Bellwork # • HW, red pen book on desk.

  26. Agenda • PA# • Workbook pp.83 & 84 • Benchmark 3 is Friday.

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