Chapter 9
Math 7
Class Notes
Areas of Triangles
Vocabulary
| o
| Perpendicular – two intersecting lines forming right angles
|
Formula
1. Area of a Triangle: A =
OR A =
bh
** IMPORTANT **
When finding area – Units are always squared.
EXAMPLES
Make sure to show the formula used and each step to receive full credit.
Label, label, label
| 1.
| Find the area of triangle ABC |
| | |
| | |
A =
A =
[show multiplication/division work – no calculator]
A =
A = 28 ft.
OR 28 ft. sq. OR 28 sq. ft.
| 2.
| Find the base of a triangle with a height of 6 inches and an area of 12 square inches. |
** Figure out what you are solving for in the formula A =
**
In this problem it is the base – so write down what you know
| A = 12 sq. in
|
| h = 6 in. PLUG IN WHAT YOU KNOW
|
| b = b
|
| |
| |
| A =
|
| |
| 12 sq. in. =
(multiply both sides by 2) OR (simplify fraction if you can)
|
| |
| 24 sq. in. = (6 in)b (divide both sides by 6 in)
|
| |
| **Reminder** - when you divide something by itself it is 1
|
| |
| 
=
[show multiplication/division work – no calculator]
|
| |
| |
| 4 in. = b
|
| |
| |
Textbook pages 254-255
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