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© 2007 M. Tallman
© 2007 M. Tallman
© 2007 M. Tallman
© 2007 M. Tallman
The area of this rectangle is 40 cm².
If you divide this rectangle in half, what two shapes do you see?
A = 40 cm²
© 2007 M. Tallman
© 2007 M. Tallman
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 = 20 cm²
A = 40 cm²
© 2007 M. Tallman
© 2007 M. Tallman
The area of this parallelogram is 64 cm².
If you divide this parallelogram in half, what two shapes do you see?
A = 64 cm²
© 2007 M. Tallman
© 2007 M. Tallman
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 = 32 cm²
A = 64 cm²
© 2007 M. Tallman
© 2007 M. Tallman
Since triangles are ½ of a rectangle or parallelogram, the formula for finding the area of
triangles is A = ½bh.
A = 8 cm × 5 cmA = 40 cm²
A = 8 cm × 5 cm
A = 20 cm²
½ ×A = 4 cm × 5 cm
© 2007 M. Tallman
© 2007 M. Tallman
Since triangles are ½ of a rectangle or parallelogram, the formula for finding the area of
triangles is A = ½bh.
A = 8 cm × 8 cmA = 64 cm²
A = 8 cm × 8 cm
A = 32 cm²
½ ×A = 4 cm × 8 cm
© 2007 M. Tallman
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 = 9 cm²
½
×A = 3 cm × 3 cm
A = 4 cm × 5 cm
A =10cm²
½
×A = 2 cm × 5 cm
A = 6 cm × 7 cm
A = 21 cm²
½
×A = 3 cm × 7 cm
© 2007 M. Tallman
© 2007 M. Tallman
The way the factors are grouped does not change the product.
The associative property can make finding the area of a triangle easier!
= 24 = 24 33 22xxxx44(( ))
(4 × 3) × 2=4 × (3 × 2)
© 2007 M. Tallman
© 2007 M. Tallman
(½ × h) × b
½½ bb(( ))AA == ×× ×× hh
(½ × b) × h=½ × (b × h)=Group the factors in which ever way
that makes the problem easier to solve.
The way the factors are grouped does not change the product.
The associative property can make finding the area of a triangle easier!
© 2007 M. Tallman
© 2007 M. Tallman
Use the formula A = ½bh to find the area of the triangle.
8 ft
A = 8 ft) × 9 ft
A = 36 ft²
9 ft
(½ ×
A = 4 ft × 9 ft
© 2007 M. Tallman
© 2007 M. Tallman
Use the formula A = ½bh to find the area of the triangle.
20 yd
A = 20 yd)× 14 yd
A = 140 yd²
14 yd
(½ ×A = 10 yd × 14 yd
© 2007 M. Tallman
© 2007 M. Tallman
Use the formula A = ½bh to find the area of the triangle.
16 m
A = 16 m) × 9 m
A = 72 m²
9 m
(½ ×A = 8 m × 9 m
© 2007 M. Tallman
© 2007 M. Tallman
Use the formula A = ½bh to find the area of the triangle.
7 in
A = 7 in × 10 in
A = 35 in²
10 in
½ ×A = 7 in × 5 in
© 2007 M. Tallman
© 2007 M. Tallman
Use the formula A = ½bh to find the area of the triangle.
11 mm
A = (11 mm×6 mm)
A = 33 mm²
6 mm
½ ×A = 11 mm × 6 mm
© 2007 M. Tallman
© 2007 M. Tallman
A =36units²
© 2007 M. Tallman
© 2007 M. Tallman
A =27.5units²
© 2007 M. Tallman
© 2007 M. Tallman
A =24units²
© 2007 M. Tallman
© 2007 M. Tallman
A =20units²
© 2007 M. Tallman
© 2007 M. Tallman
A = 9 units²
© 2007 M. Tallman
© 2007 M. Tallman
A =16units²
© 2007 M. Tallman
© 2007 M. Tallman
A =21units²
© 2007 M. Tallman
© 2007 M. Tallman
6 mm
8 mm
b
A = 24 mm²
24 mm² × =2 48 mm²
48 mm² ÷ 8 mm = 6 mm
© 2007 M. Tallman
© 2007 M. Tallman
8.5 fth
14 ft
A = 59.5 ft²
59.5 ft² × =2 119 ft²
119 ft² ÷ 14 ft = 8.5 ft
© 2007 M. Tallman
© 2007 M. Tallman
12 inb
9 in
A = 54 in²
54 in² × =2 108 in²
108 in² ÷ 9 in = 12 in
© 2007 M. Tallman
© 2007 M. Tallman
11.5 ft
7 ft
h
A = 40.25 ft²
40.25 ft² × =2 80.5 ft²
80.5 ft² ÷ 7 ft = 11.5 ft
© 2007 M. Tallman
© 2007 M. Tallman
8 ydb
A = 48 yd²
48 yd² × =2 96 yd²
96 yd² ÷ 12 yd= 8 yd
12 yd
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