1. Area of Triangles and Trapezoids

2. Bell Ringer-Tuesday

3. Area of Triangles and Trapezoids
Course 2
9-4
Area of Triangles and Trapezoids
AREA OF A TRIANGLE
The area A of a triangle
is half the product of its
base b and its height h. 1 2
A = bh h b

4. Additional Example 1A: Finding the Area of a Triangle
Course 2
9-4
Area of Triangles and Trapezoids
Additional Example 1A: Finding the Area of a Triangle
Find the area of the triangle. 1 2
A = bh
Use the formula. 5 1 2
Substitute 8 for b and
5 for h.
A =
(8 · 5) 8
A = 20
The area of the triangle is 20 square units.

5. Additional Example 1B: Finding the Area of a Triangle
Course 2
9-4
Area of Triangles and Trapezoids
Additional Example 1B: Finding the Area of a Triangle
Find the area of the triangle. 1 2
A = bh
Use the formula. 12 1 2
A =
(9 · 12) 9

6. Area of Triangles and Trapezoids
Course 2
9-4
Area of Triangles and Trapezoids
Check It Out: Example 1B
Find the area of the triangle. 1 2
A = bh

7. Area of Triangles and Trapezoids
Course 2
9-4
Area of Triangles and Trapezoids
The two parallel sides of a trapezoid are its bases, b1 and b2. The height of a trapezoid is the perpendicular distance between the bases. b2 h b1

8. Area of Triangles and Trapezoids
Course 2
9-4
Area of Triangles and Trapezoids
AREA OF A TRAPEZOID b2
The area of a trapezoid is half its height multiplied by the sum of its two bases. 1 2 A =
h(b1 + b2) h b1
In the term b1, the number 1 is called a subscript. It is read as “b-one” or “b sub-one.”
Reading Math

9. Additional Example 2A: Finding the Area of a Trapezoid
Course 2
9-4
Area of Triangles and Trapezoids
Additional Example 2A: Finding the Area of a Trapezoid
Find the area of the trapezoid.
5 in. 1 2
A =
h(b1 + b2)
Use the formula. 1 2
A =
· 6(5 + 9)
6 in.
Substitute. 1 2
A =
· 6(14)
Add.
9 in.
A = 42
Multiply.
The area of the trapezoid is 42 in2.

10. Area of Triangles and Trapezoids
Course 2
9-4
Area of Triangles and Trapezoids
Check It Out: Example 2A
Find the area of the trapezoid. 1 2
A =
h(b1 + b2)
Use the formula. 1 2
A =
· 6( )
Substitute.
11.2 in.
4.3 in.
6 in.
Add.
Multiply.

11. Additional Example 3: Geometry Application
Course 2
9-4
Area of Triangles and Trapezoids
Additional Example 3: Geometry Application
The state of Wisconsin is shaped somewhat like a trapezoid. What is the approximate area of the state? 1 2
A =
h(b1 + b2)