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

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Presentation on theme: "Area: Triangles and Trapezoids Lesson 10-2 p.509 1. Start the Bellwork Quiz. 2. Have your HW, red pen, and book on your desk."— Presentation transcript:

1 Area: Triangles and Trapezoids Lesson 10-2 p Start the Bellwork Quiz. 2. 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 = bhor A = bh 2

4 Triangles  Let’s look at an example: 4 feet 5 feet A = bh = 4 (5) = or 10 ft 2

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

6 Try This  Find the areas: 12 in. 3 ft. 5 mi. 6 miles 7 miles 216 in 2 or 1.5 ft 2

7 Try This  Find the areas: 12 in. 3 ft. 5 mi. 6 miles 7 miles 216 in 2 or 1.5 ft 2 15 mi 2

8 Trapezoids  Trapezoids have different formula. It looks like this:  A = h (b 1 + b 2 ) or A = h(b 1 + b 2 ) 2 b1b1 b2b2 h

9 Trapezoids  A = h (b 1 + b 2 ) or A = h(b 1 + b 2 ) 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. b1b1 b2b2 h

10 Trapezoids  Let’s try an example:  A = h (b 1 + b 2 ) A = 3.5 (4 + 6) 2 2 A = 3.5 (5) = 17.5 ft 2 4 ft 6 feet 3.5 ft

11 Try This  Find the area: 24 mm 33 mm 12 mm

12 Try This  Find the area: 24 mm 33 mm 12 mm 342 mm 2

13 Try This  Find the area: 4 feet 2 feet 4.5 feet

14 Try This  Find the area: 4 feet 2 feet 4.5 feet 13 ft 2

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

18 Try This  Find the area: 4 cm 6 cm 8 cm 6 cm

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

20 Try This  Here is a hint: 4 cm 6 cm 8 cm 6 cm For the rectangle: A = bh A = 6 (4) = 24 cm 2 For the trapezoid: A = ½ h (b 1 + b 2 ) A = ½ (2) (4 + 6) A = 10 cm 2 Total area = = 34 cm 2

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

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

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

24 Agenda  PA#38  Pp #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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