Transcript Chapter 7 Lesson 4 - Mrs.Lemons Geometry

Chapter 7 Lesson 4
Objective: To find the area of a
trapezoid.
height of a trapezoid: the perpendicular distance h between
the bases.
Base
Leg
h
b1
b2
Leg
Base
Theorem7-10: Area of a Trapezoid
The area of a trapezoid is half the product of the height and
the sum of the bases.
b1
1
A  h (b1  b2 )
2
h
b2
Example 1:
Find Area of a Trapezoid
Find the area of a trapezoid with height 7 cm and bases 12
cm and 15 cm.
1
A  h (b1  b2 )
2
A
1
(7 )(12  15)
2
A
1
(7)(27 )
2
A  (3.5)(27)
A  94.5cm2
Example
2:
Find Area of a Trapezoid
Find the area of a trapezoid with height 18 cm and bases
20 cm and 36 cm.
1
A  h (b1  b2 )
2
A
1
(18)(20  36)
2
A
1
(18)(56)
2
A  (9)(56)
A  504cm2
Example 3:
Finding Area Using a Right Triangle
Find the area of the trapezoid. Leave your answer in simplest
5cm
radical form.
Since you do not
1
A  h (b1  b2 ) have the height of
the trapezoid we
h
2
will have to draw it
in.
60°
Find h.
LL  3  SL
h  3 2
h 2 3
Find area.
1
(2 3 )(7  5)
2
1
A  (2 3 )(12)
2
A
A  (1 3)(12)
A  12 3cm2
2cm
7cm
5cm
Example 4:
Finding Area Using a Right Triangle
Find the area of the trapezoid. Leave your answer in simplest
radical form.
11cm
Since you do not
1
A  h (b1  b2 ) have the height of
the trapezoid we
h
2
will have to draw it
in.
Find h.
LL  3  SL
h  3 5
h 5 3
Find area.
1
(5 3 )(11  16)
2
1
A  (5 3)(27 )
2
A
A  (2.5 3)(27)
A  67.5 3cm2
60°
5cm
16cm
11cm
Homework
Page 376-377
#1-13;21;22;24-27