Areas of Triangles, Parallelograms, &
Trapezoids
RectangleArea = number of square units contained in the figure.
Calculated A = lw
l
w
Rectangle
Sometimes referred to as base and height
A = bh
b
h
Parallelogram
Especially, when we are looking at a parallelogram
A = bh
b
h
Parallelogram
Height is always PERPENDICULAR to the base
A = bh
b
h
Triangles
Now let’s consider triangles
b
h
How would we calculate the Area of the triangle?
Triangles
A = ½ bh
b
h
Triangles
No matter what the triangle looks like, A = ½ bh.
bh h
b
h
bh
b
Triangles
Folding the corners over shows that the triangle is ½ the rectangle.
h
b
Trapezoids
A = ½ h (b1 + b2)
h
b1
b2
Sample problems
Identify the shape and use the appropriate formula.
8 cm
12 cm
Sample problems
A = lwA = 8 12
8 cm
12 cm
96 cm2
Sample problems
Identify the shape and use the appropriate formula.
15’
9’
Sample problems
A = b hA = 15 9
15’
9’
135 ft2
Sample problems
Identify the shape and use the appropriate formula.
14”
Sample problems
A = s2
A = 142
196 in214”
Sample problems
Identify the shape and use the appropriate formula.
5cm
24 cm
Sample problems
A = ½ b hA = ½ 24 5
5cm
24 cm
60 cm2
Sample problems
Identify the shape and use the appropriate formula.
15 m
12 m6 m
Sample problems
A = ½ h (b1 + b2)
A = ½ 6 (12 + 15) 12
m
15 m
6 m81 m2
Sample problems
Identify the shape and use the appropriate formula.
5 m
Sample problems
What is the height?
5 m