why is a right triangle called aright triangle?

Answer 1

There are many sites giving an etymology of "right angle". I liked best this one by Pat Bellew:

"The Latin word for the Greek term ortho, was rectus which was also used to mean both straight and erect. We see the imprint of rectus in many math words and common language with both the straight and erect meanings. The rectum is so called because it is the "straight intestine", while a rectangle is a parallelogram with an "erect angle". In fact, the word rectangle was sometimes used for a "right angle" into the 19th century."

"The latus rectum in a parabola is the side (latus) through the focus that is straight (rectus - parallel to the directrix). Latus rectum is the Latin translation of the Greek orthea pleura for erect side which was the term Apollonius used in his books on the conic sections. As languages blended in the middle ages, rectos became "recht" and eventually became our word for "right" and for the right angle."

A right triangle has been defined as a triangle with a right angle

Answer 2

when you make a right turn or a left turn, it is usually a 90-degree turn. as the triangle also has a 90-degree corner, it is called a right triangle.

Answer 3

because one angle is 90 degrees and that's just what they call a triangle with a 90 degree angle

Answer 4

Because theres no such thing as a wrong one.