1. Let’s Talk Triangles & Parallelograms

2. These are parallelograms!

3. Area of a Parallelogram
quadrilateral
A parallelogram is a _______________
whose opposite sides are _________.
Area of a parallelogram =
parallel
base x height
Since a rectangle is a type of parallelogram, the area formula is exactly the same!!

4. Let’s talk about height for a moment…
Select two students and measure their heights

5. What is the height of each parallelogram?
4 cm
5 cm
4 ft
8 ft
13 cm
5 ft
2 in
12 in
9 in

6. Area of a parallelogram:
A = bh
Which measurements will we use?
Fill in the formula
Write your answer and label your units.
h = 4 ft
5 ft
4 ft
b = 8 ft
8 ft
5 ft is not the height!! We won’t use this in our area calculation!
A =
(4)(8)
= 32
A = 32ft2

7. Area of a parallelogram:
A = bh
Which measurements will we use?
Fill in the formula
Write your answer and label your units.
h = 8 ft
12 ft
8 ft
b = 20 ft
20 ft
A =
(8)(20)
= 160
A = 160 ft2

8. Area of a parallelogram:
A = bh
Which measurements will we use?
Fill in the formula
Write your answer and label your units.
h = 6 in
7 in
6 in
b = 5 in
5 in
A =
(6)(5)
= 30
A = 30 in2

9. 1) 2) 3) Calculate the area: 5 ft 7 ft 8 ft 1.5 in 5 in 2.5 in
10.05 cm 3)
3.4 cm
6.5 cm

10. Let’s examine something…
A triangle can be thought of as half of a parallelogram.

11. What would be the formula for the area of a triangle?
Riddle me this…
We just calculated how to find the area of a parallelogram.
A = bh
If a triangle is simply half of a parallelogram, then…
What would be the formula for the area of a triangle?

12. If we have a parallelogram…
A = bh
8(3)
= 24 ft2
3 ft
4 ft
8 ft
What is the area of just this triangle?
= 12 ft2

13. Area of a triangle AREA OF A TRIANGLE Words Numbers Formula
Triangle: The area A of a triangle is one-half the base length b times the height h.
A = (8)(4)
= 16 units2
1 2

14. A = Area of a triangle: A = 16 ft2 h = 4 ft b = 8 ft (4)(8) = (32)
Which measurements will we use?
Fill in the formula
Write your answer and label your units.
h = 4 ft
4 ft
b = 8 ft
8 ft 1 1
A =
(4)(8) =
(32)
= 16 2 2
A = 16 ft2

15. A = Area of a triangle: A = 75 in2 h = 10 in b = 15 in (10)(15) =
Which measurements will we use?
Fill in the formula
Write your answer and label your units.
h = 10 in
10 in
b = 15 in
15 in 1 1
A =
(10)(15) =
(150)
= 75 2 2
A = 75 in2

16. A = Area of a triangle: A = 30 cm2 h = 5 cm b = 12 cm (5)(12) = (60)
Which measurements will we use?
Fill in the formula
Write your answer and label your units.
14 cm
h = 5 cm
6 cm
5 cm
b = 12 cm
12 cm 1 1
A =
(5)(12) =
(60)
= 30 2 2
A = 30 cm2

17. A = Area of a triangle: A = 33 ft2 h = 6 ft b = 11 ft (6)(11) = (66)
Which measurements will we use?
Fill in the formula
Write your answer and label your units.
14 ft
h = 6 ft
6 ft
b = 11 ft
11 ft 1 1
A =
(6)(11) =
(66)
= 33 2 2
A = 33 ft2

18. 1) 2) 3) Calculate the area: 5 in 3 in 12 in 4.5 ft 2.3 ft 8.7 cm

19. Keypoint!
The base of a triangle is not always the
bottom side!!!

20. Let’s try one!
Graph and find the area of the figure with the given vertices.
(–2, 2), (4, 2), (0, 5)
Area of a triangle
A = bh 1 2
(0, 5)
Substitute for b and h.
= • 6 • 3 1 2
(–2, 2)
(4, 2) 6
= 9 units2