Notes
triangle

Triangle

A triangle is a polygon with three sides.

Types of Triangle

Angles in a Triangle

The interior angles in a triangle add up to $180^\circ$ .

Area of a Triangle

There are several ways to calculate the area of a triangle.

Choose one side as the “base” and measure the “height” of the third vertex above this base. Then the area is $\frac{1}{2} \times \text{base} \times \text{height}$ .
Let $a$ and $b$ be the lengths of two of the sides and $C$ the angle between them. Then the area is $\frac{1}{2} a b \sin(C)$ .
Let $s$ be the semi-perimeter (that is, half the perimeter). And let $a$ , $b$ , $c$ be the side lengths. Then the area is $\sqrt{s(s - a)(s - b)(s - c)}$ .

category: angle facts

category: shapes

Revised on June 23, 2021 21:57:16 by Andrew Stacey

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