A triangle is a three-sided polygon also known as a figure. The sum of the angles in a triangle is always 180 degrees. Triangles are classified according to their angles and sides.

The sum of the lengths of the sides of a triangle is always greater than the length of the longest side.

The triangles with the largest possible area for a given perimeter are equilateral triangles, in which all three sides have equal lengths. Isosceles and scalene triangles are two other types of common triangles.

There are three main types of triangles when discussing angles: acute, obtuse, and right triangles.

1) Acute triangles have all three angles less than 90 degrees.

2) Obtuse triangles have one angle greater than 90 degrees.

3) Right triangles have one angle that is exactly 90 degrees; this angle is called the right angle or hypotenuse angle. The side opposite the right angle is always the longest side of a right triangle, and it is called the hypotenuse. The other two sides are called legs.