## Area of a Triangle Lesson

#### Introduction

A triangle is a three-sided polygon. Triangles are one of the most basic geometric shapes, and their properties can be used to determine the area of many other polygons. A right triangle is a triangle which has one 90 degree angle between sides. An equilateral triangle is a triangle which has three sides of equal length with equal angles between them. An Isosceles triangle is a triangle which has two equal sides and two equal angles.

#### Terms

**Area**- A quantity that expresses the extent of a two-dimensional shape.

**Triangle**- A polygon with three sides.

**Polygon**- A plane figure with at least three sides.

**Right Triangle**- A triangle where one angle is a right angle (90 degrees).

**Isoceles Triangle**- A triangle with two equal sides.

**Equilateral Triangle**- A triangle with three equal sides.

## Lesson

The formula for the area of a triangle is:

$ext{Area} = dfrac{a*h}{2}$

where a is the length of the base, and h is the height. You can think of the area of a triangle as being half of the area of a rectangle with sides a and h.

If a rectangle has a base of length 3 and height of 4, for example, the area is

$ext{Area} = dfrac{a*h}{2}$

$ext{Area} = dfrac{3*4}{2}$

$ext{Area} = dfrac{12}{2}$

$ext{Area} = 6$