Triangles are one of the fundamental figures used in Euclidean geometry. There are three elements needed to make one. It is a

Trilateral plane or two-dimensional figure, in which the sum of the interior angles equals exactly 180 degrees.

There are two common triangle classification systems. One focuses on the sides and designates three types.

Equilateral triangle. Equilateral means “equal sides”, and in an equilateral triangle, all three sides are the same length. This means the angles will also be equal – all 60° – making them equiangular as well.

Isosceles triangle. Isosceles means “equal legs” and this type has two sides that are equal in length. This also means that the two angles formed where the equal sides meet the third side are equal.

Scalene triangle. Scalene comes from a word meaning “unequal” and this type has three unequal sides. As you might suspect, then, the three angles are also unequal.

The other triangle classification scheme addresses shapes from the point of view of the measures of the interior angles. It also designates three types.

Acute triangle. In an acute triangle, the largest interior angle is acute – less than 90°. This means that all angles are acute.

Right triangle. In this type, there is a right angle – an angle of exactly 90°. This means that the other two angles will be acute.

Obtuse triangle. This shape has an internal angle that is obtuse. This again means that the other two angles will be acute.

A triangle has three sides.

Other triangles. The word triangle is also used for things that bear some resemblance to this shape, either by having the approximate shape or by having three points that are connected in some way. The musical instrument called the triangle is a metal rod with three sides, except one corner is open. It is hung from a thin wire so that it can vibrate when hit by a beater. It is used in orchestral and band music. A so-called love triangle is a romantic situation that involves three people and usually implies that each person prefers a partner.

A musical triangle is a metal rod with three sides.

Triangle is also used in reference to places that have a more or less triangular shape. The Bermuda Triangle, the area roughly bounded by Bermuda, Fort Lauderdale, and Puerto Rico, is a well-known part of the planet because it has a reputation for unexplained disappearances. There are several Golden Triangles, including the area of Southeast Asia known for its opium production, however, a golden triangle is also an isosceles triangle constructed in such a way that the ratio of the hypotenuse to the base is equal to the so-called golden ratio, so we close the circle back to math.