1. Area of
Triangles

2. A = 40 cm² The area of this rectangle is 40 cm².
If you divide this rectangle in half, what two shapes do you see?
A = 40 cm²

3. A = 40 cm² A = 20 cm² The area of this rectangle is 40 cm².
If you divide this rectangle in half, what two shapes do you see?
Triangles
So if the rectangle’s area is 40 cm², what is ½ of the rectangle’s area?
20 cm²
A = 40 cm²
A = 20 cm²

4. A = 64 cm² The area of this parallelogram is 64 cm².
If you divide this parallelogram in half, what two shapes do you see?
A = 64 cm²

5. A = 64 cm² A = 32 cm² The area of this parallelogram is 64 cm².
If you divide this parallelogram in half, what two shapes do you see?
Triangles
So if the parallelogram’s area is 64 cm², what is ½ of the parallelogram’s area?
32 cm²
A = 64 cm²
A = 32 cm²

6. Area A = 8 cm × 5 cm A = 40 cm² A = ½ × 8 cm × 5 cm A = 4 cm × 5 cm A
Since triangles are ½ of a rectangle or parallelogram, the formula for finding the area of triangles is A = ½bh. A =
8 cm ×
5 cm A = 40
cm² A = ×
8 cm ×
5 cm A =
4 cm ×
5 cm A = 20
cm²

7. Area A = 8 cm × 8 cm A = 64 cm² A = ½ × 8 cm × 8 cm A = 4 cm × 8 cm A
Since triangles are ½ of a rectangle or parallelogram, the formula for finding the area of triangles is A = ½bh. A =
8 cm ×
8 cm A = 64
cm² A = ×
8 cm ×
8 cm A =
4 cm ×
8 cm A = 32
cm²

8. Area of a Triangle ½ A = × 6 cm × 3 cm A = 3 cm × 3 cm A = 9 cm² ½ A =
If you know the base (b) and the height (h) of a triangle, you can use a formula to find its area.
If you multiply the ½ × b × h, you get the area (A).
A = ½ × b × h or
A = ½bh A = ×
6 cm ×
3 cm A =
3 cm ×
3 cm A = 9
cm² A = ×
4 cm ×
5 cm A =
2 cm ×
5 cm A = 10
cm² A = ×
6 cm ×
7 cm A =
3 cm ×
7 cm A = 21
cm²
© 2007 M. Tallman

9. ( ) 4 x 3 x 2 = 24 (4 × 3) × 2 = 4 × (3 × 2) Associative Property
The way the factors are grouped does not change the product.
The associative property can make finding the area of a triangle easier! ( ) 4 x 3 x 2
= 24
(4 × 3) × 2 =
4 × (3 × 2)

10. A = ( ) ½ × b × h (½ × b) × h = ½ × (b × h) = (½ × h) × b
Associative Property
The way the factors are grouped does not change the product.
The associative property can make finding the area of a triangle easier! A = ( ) × b × h
(½ × b) × h =
½ × (b × h) =
(½ × h) × b
Group the factors in which ever way that makes the problem easier to solve.

11. Use the formula A = ½bh to find the area of the triangle.
(½ ×
8 ft) ×
9 ft A =
4 ft ×
9 ft A = 36
ft²

12. Use the formula A = ½bh to find the area of the triangle.
14 yd
20 yd A =
(½ ×
20 yd) ×
14 yd A =
10 yd ×
14 yd A =
140
yd²

13. Use the formula A = ½bh to find the area of the triangle.
(½ ×
16 m) ×
9 m A =
8 m ×
9 m A = 72 m²

14. Use the formula A = ½bh to find the area of the triangle.
½ ×
7 in ×
10 in A =
7 in ×
5 in A = 35
in²

15. Use the formula A = ½bh to find the area of the triangle.
6 mm
11 mm A =
½ ×
(11 mm ×
6 mm) A =
11 mm ×
6 mm A = 33
mm²

16. Find the Area A = 36
units²

17. Find the Area A =
27.5
units²

18. Find the Area A = 24
units²

19. Find the Area A = 20
units²

20. Find the Area A = 9
units²

21. Find the Area A = 16
units²

22. Find the Area A = 21
units²

23. Find the Missing Measurement
A = 24 mm²
24 mm² × 2 =
48 mm²
48 mm² ÷
8 mm =
6 mm
8 mm b
6 mm

24. Find the Missing Measurement
A = 59.5 ft²
8.5 ft h
14 ft
59.5 ft² × 2 =
119 ft²
119 ft² ÷
14 ft =
8.5 ft

25. Find the Missing Measurement
A = 54 in²
9 in
12 in b
54 in² × 2 =
108 in²
108 in² ÷
9 in =
12 in

26. Find the Missing Measurement
A = ft² h
11.5 ft
7 ft
40.25 ft² × 2 =
80.5 ft²
80.5 ft² ÷
7 ft =
11.5 ft

27. Find the Missing Measurement
A = 48 yd²
48 yd² × 2 =
96 yd²
96 yd² ÷
12 yd =
8 yd
12 yd
8 yd b