Triangle facts
 For other meanings, such as the musical instrument that is also called a "triangle", see triangle (disambiguation).
A triangle is a shape, or a specific part of two dimensional space. It has three straight sides and three vertices. The three angles of a triangle always add up to 180° (180 degrees). It is the polygon with the least possible number of sides.
Contents
Types of triangles
Triangles can be grouped according to how long their sides are:
 if all the three sides of a triangle have the same length, then we have an equilateral triangle;
 if a triangle has two sides with the same length, then we have an isosceles triangle;
 if all the three sides of a triangle have different lengths, then we have a scalene triangle.
Triangles can also be grouped by their angles:
 if a triangle has a right angle, that is, if one of the angles of that triangle measures 90° (90 degrees), then we have a right triangle. The opposite side to the right angle is the hypotenuse;
 if a triangle has an obtuse angle, that is, if one of the angles of that triangle is larger than 90°, then we have an obtuse triangle;
 if a triangle has only acute angles, that is, if all the angles of that triangle are less than 90°, then we have an acute triangle.

Uses
Triangles are extremely useful. Measuring objects using triangles is called trigonometry. Some people have spent their entire lives studying triangles for use in trigonometry.
Modern computers usually use triangles to make more complex graphic images or shapes.
Related pages
Images

The Flatiron Building in New York is shaped like a triangular prism
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Triangle Facts for Kids. Kiddle Encyclopedia.