A triangle is a polygon. It is a closed 3-sided shape made up of straight lines. The ‘tri-’ part of the word triangle means three. A triangle has 3 sides and 3 angles. Interior angles are the angles ...

https://doi.org/10.4169/college.math.j.47.5.356 https://www.jstor.org/stable/10.4169/college.math.j.47.5.356 This paper provides a new, long proof of the Pythagorean ...