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 180 180^\circ.

Area of a Triangle

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

  1. Choose one side as the “base” and measure the “height” of the third vertex above this base. Then the area is 12×base×height\frac{1}{2} \times \text{base} \times \text{height}.

  2. Let aa and bb be the lengths of two of the sides and CC the angle between them. Then the area is 12absin(C)\frac{1}{2} a b \sin(C).

  3. Let ss be the semi-perimeter (that is, half the perimeter). And let aa, bb, cc be the side lengths. Then the area is s(sa)(sb)(sc)\sqrt{s(s - a)(s - b)(s - c)}.

category: angle facts
category: shapes