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