Triangles

A triangle is a polygon with three sides and three angles. The sum of the interior angles of any triangle is always 180 degrees. Triangles are fundamental in geometry because any polygon can be divided into triangles, and many geometric properties are based on triangles.

Important properties

• The sum of the interior angles is 180 degrees.

• The triangle inequality: the sum of the lengths of any two sides is greater than the third side.

• Classification by sides: equilateral (all sides equal), isosceles (two sides equal), scalene (all sides different).

• Classification by angles: acute (all angles < 90°), right (one angle = 90°), obtuse (one angle > 90°).