1. Area of Right Triangles

2. Warm Up A = b x h A = 25 x 8 height A = 200 ft2 base
OBJECTIVE: SWBAT determine the area of any right triangle and defend their method.
1) What is the Area of the Parallelogram below?
A = b x h
A = 25 x 8
A = 200 ft2
10 ft
8 ft
height
base
25 ft
Calculate
(Click for Detailed Solutions)

3. Getting Ready– Puzzle!
1) How many rectangles can you find? What are their areas?
Hints

4. Getting Ready – Puzzle!
2) How many shapes can you find? Name them if you can.
Hints

5. Launch This is a right triangle. What is a right triangle?
A right triangle is a triangle that has one 90⁰ angle.
What is the area of this right triangle? How do you know?
How can you show your work/prove your answer?
= 1 square unit

6. Launch What is the area of the shaded region? How do you know?
How can you show your work/prove your answer?

7. Explore – Understanding the Strategy
Angela’s Strategy
Draw a “surrounding rectangle”
Determine the area of the rectangle
The area of the triangle is half the area of the rectangle!
Do you understand Angela’s strategy?

8. Explore - More Part 3 - (10 Min) Finish the worksheet in GROUPS
Use Angela’s Strategy to find the area of the remaining triangles on the worksheet.
1-Partners
2-Strategy Check
3-Groups

9. Summary – Complete 1 – 14 with your group – showing all of your work.9)
10)
11) 1) 2) 4) 3)
12)
13)
14) 5) 6) 7) 8)
To Explore

10. Summary (Part 2) Explain the Strategy Turn and Talk: Common Language:
Lefty, tell Righty the strategy for finding the area of ANY right triangle.
Righty, tell Lefty the strategy.
Common Language:
Can you explain the strategy we learned that will work for finding the area of ANY right triangle?
Why does this strategy work?

11. Summary (Part 2) Expand your Thinking
Does this strategy work when there are no grid lines?

12. Area of “Rectangle”: 5 ft x 10 ft = 50 ft2 Area of Triangle
Summary (Part 2)
Draw and label a triangle with a base of 5 ft and a height of 10 ft. Then find the area.
Area of “Rectangle”:
5 ft x 10 ft = 50 ft2
Area of Triangle
50 ft2 ÷ 2 = 25 ft2
10 ft
Oh yeah…
Half of 50 is 25!
5 ft
Hmmm…

13. Summary (Part 2) Practice – in your journal
#1) Draw and label a triangle with a base of 8 in and a height of 3 in. Then find the area.
Area of “Rectangle”:
8 in x 3 in = 24 in2
Area of Triangle
24 in2 ÷ 2 = 12 in2
3 in
8 in
Oh yeah…
Half of 24 is 12!
Hmmm…

14. Summary (Part 2) Practice – in your journal
#2)
8 ft
5 ft
Rectangle area = ______
Triangle area = ______
#3)
12 m
4 m
Triangle area = _______
Rectangle area = ______
40 ft2
48 m2
20 ft2
24 m2

15. Complete 15 – 17 with your group.
Should everyone’s triangle look the same?
Do they need to??

16. Exit Ticket - in your journal
4 cm
What is the area of the “Surrounding Rectangle” for this Right Triangle?
9 cm
13 cm2
18 cm2
36 cm2
d) 25 cm2

17. Exit Ticket - in your journal
4 cm
What is the area of the Triangle?
9 cm
4 ½ cm2
18 cm2
36 cm2
d) 11 cm2