## Basic Rules of Triangles

There are some rules that are true for all the different kinds of triangles. Below are the four most important rules. Note: The triangles in the figures represent any triangle.

- The sum of the interior angles of a triangle is 180°.

x° + y° + z° = 180° - The length of the longest side of a triangle must be less than the sum of the lengths of the other two sides of the triangle, but greater than the difference of the lengths.

(AB – BC) < AC < (AB + BC) - The longest side of a triangle is opposite the largest angle and the shortest side is opposite the smallest angle.

∠B is the largest angle so AC is the longest side.

AB is the shortest side so ∠C is the smallest angle. - If you extend one side of the triangle, the exterior angle formed will be equal to the sum of the other two interior angles in the triangle.

x° + z° = n°