Finding the area of a trapezoid
Finding the area of a trapezoid
1
Finding the area of a trapezoid
8cm
4cm
4.5cm
5.5cm
6cm
What is the length of the height of this trapezoid?
What is the length of the base of this trapezoid?
2
Finding the area of a trapezoid
Area of a trapezoid
8cm
4cm
4.5cm
5.5cm
6cm
We will use the trapezoid from the last slide.
3
Finding the area of a trapezoid
The area of a trapezoid
6cm
+
8cm
4cm
4.5cm
6cm
+
8cm
We take a copy of the trapezoid and create a parallelogram.
What is the base of this parallelogram?
What is the height of this parallelogram?
4
Finding the area of a trapezoid
The area of a trapezoid
6cm
+
8cm
4cm
4.5cm
6cm
+
8cm
We take a copy of the trapezoid and create a parallelogram.
What is the base of this parallelogram? 14 cm
What is the height of this parallelogram? 4 cm
How do these compare to the dimensions of the original trapezoid?
5
Finding the area of a trapezoid
The area of a trapezoid
8cm
4.5cm
+
6cm
4cm
We learned yesterday that the Area of a parallelogram = bh.
So the area of the above paralellogram = (sum of the two bases of the trapezoid)(height of the trapezoid)
6
Finding the area of a trapezoid
The area of a trapezoid
8cm
4.5cm
+
6cm
4cm
This parallelogram represents two of the original trapezoids.
What would the area of one of the trapezoids be equal to?
7
Finding the area of a trapezoid
The formula for the area of a trapezoid:
1 (b + b )h
• Area of trapezoid = 2
2 1
Length of first base
of trapezoid
height of trapezoid
Length of second base
of trapezoid
8
Finding the area of a trapezoid
Sketch the following quadrilateral and determine its area.
A trapezoid with bases of 13 feet and 10 feet and a height of 6 feet.
9
Finding the area of a trapezoid
Sketch the following quadrilateral and determine its area.
A trapezoid with bases of 13 feet and 10 feet and a height of 6 feet.
(b + b )h
1
2
10ft
A =
2
6ft
= (13ft + 10ft)6ft
2
13ft
23(6) 2
ft
=
2
2
= 138 ft
2
2
= 69 ft
10