Section 11-5: Areas of Triangles & Trapezoids
Pg.558
Objective & Vocabulary1. Find the areas of triangles and trapezoids.
Triangles• Base of a triangle (pg.558): the length of any one of the
sides.• Height of a triangle (pg.558): the perpendicular distance
between the base and the vertex opposite that side.• Area of a triangle (pg.558): The product of ½ the base and
height (A= ½ bh).
Height h
Base b
Height h
Base b
Example 1: Finding the Area of a Triangle
A. Find the area of the following triangle.
B. Find the area if the base is 9in and the height is 6in.
Example2: Finding the Base/Height of a Triangle
A. A triangle has a height of 10 cm and an area of 35 sq. cm. Find the base of the triangle.
B. Find the height of a triangle if the base is 11 m and the area is 61.6 sq. m.
Trapezoids
• Bases of a trapezoid (pg.559): the lengths of the parallel sides of a trapezoid.
• Height of a trapezoid (pg.559): the perpendicular distance between the bases.
• Area of a trapezoid (pg.559): half the product of the sum of the bases and the height [A= ½ (b1 + b2)h].
Base b2 Base b2
Base b1
Base b1
Height hHeight h
Example 3: Finding the Area of a Trapezoid
A. Find the area of the trapezoid shown.
B. Find the area of a trapezoid if the bases are 13 in and 15 in, and the height is 6 in.
Homework Time—Yea!!
Pg.560-561(1-15all, 22-25all)