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

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

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

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
12 mm
342 mm2
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 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 =
= 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 or
34 cm2
6 cm
4 cm
8 cm

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.