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)