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Lesson 10-5 Pages 520-525
Area: Parallelograms, Triangles, and
TrapezoidsLesson Check 10-4
What you will learn!
How to find the area of parallelograms, triangles, and
trapezoids.
BaseBaseAltitudeAltitude
What you really need to know!
The area A of a parallelogram equals the product of its base b and its height h. A = bh
BASE (b)
HEIGHT (h)
The area of a parallelogram is the same as the area of a rectangle!
What you really need to know!
The area A of a triangle equals half the product of its base b and height h. A = ½bh
BASE (b)
Height (h)
The area of a triangle is the same as ½ the area of a parallelogram!
What you really need to know!The area A of a trapezoid equals half the product of the height h and the sum of the bases a and b. A = ½ h(a+b)
a
bh
Notice how the top layer and bottom layer of the trapezoids creates the base of the parallelogram!
The area of a trapezoid is the same as ½ the area of a parallelogram!
bhah2
1
2
1
h
h
a
b
)(2
1bah
Example 1:
Find the area of the parallelogram.
A = bh
A = 3 x 3
A = 9 m2
Example 2:
Find the area of the parallelogram.
A = bh
A = 6.2 x 4.3
A = 26.66 in2
Example 3:
Find the area of the triangle.
A = ½ bh
A = ½ x 3 x 4
A = 6 m2
Example 4:
Find the area of the triangle.
A = ½ bh
A = ½ x 3.9 x 6.4
A = 12.48 ft2
Example 5:
Find the area of the trapezoid.
A = ½ h(a+b)
A = ½ x 6(7 ½ + 5 ¼ )
A = 38 ¼ m2
Example 6:
A wall that needs to be painted is 16 feet wide and 9 feet tall. There is a doorway that is 3 feet by 8 feet and a window that is 6 feet by 5 ½ feet. What is the area to be painted?
Area of Area of wallwall
Area of Area of doorwaydoorway
Area of Area of windowwindow
A = bhA = bh
A = 16 x 9A = 16 x 9
A = 144A = 144
A = bhA = bh
A = 3 x 8A = 3 x 8
A = 24A = 24
A = bhA = bh
A = 6 x 5 ½ A = 6 x 5 ½
A = 33A = 33
Area to be painted is:
144 – 24 – 33 = 87 ft2
Page 523
Guided Practice
#’s 3-6
Pages 520-523 with someone at home and
study examples!
Read:
Homework: Pages 524-525
#’s 8-22 even, 24-28, 32-43
Lesson Check 10-5
Page
749
Lesson 10-5
Lesson Check 10-5
