Triangle their internal angles, measured here in degrees. A triangle that has two angles with the same measure also has two sides with the same length, and therefore it is an isosceles triangle. It follows that in a triangle where all angles have the same measure, all three sides have the same length, and such a triangle is therefore equilateral. Triangles are assumed to be two-dimensional plane figures, unless the context provides otherwise (see Non-planar triangles, below). In rigorous treatments, a triangle is therefore called a "2-simplex" (see also Polytope). Elementary facts about triangles were presented by Euclid in books 1–4
Laundry symbol in the triangle prohibit chlorine bleaching. A crossed triangle prohibits any bleaching. A "circle in the square" symbolizes a clothes dryer. One dot requires drying at reduced temperature and two dots for normal temperature. The crossed symbol means that the clothing does not tolerate machine drying. In the U.S. and Japan, there are other icons for natural drying. The "iron" with up to three dots allows for ironing. The number of dots are assigned temperatures: one prescribes 110°C, two for 150°C and three for 200°C. An iron with a cross prohibits ironing. A "circle" identifies the possibilities of professional cleaning.