Euclidean Definitions

Definitions of line, perpendicular lines, and triangles

Euclid defined a line as a breadthless length. He defines a straight line as a line which lies evenly with the points on its self.

Definition number 10 in "The Elements" states, "When a straight line standing on a straight line makes the adjacent angles equal to one another, each of the equal angles is right, and the straight line standing on the other is called a perpendicular to that on which it stands."

Definition number 20 in "The Elements" wrote, "Of trilateral figures, an equilateral triangle is that which has its three sides equal, an isosceles triangle that which has two of its sides alone equal, and a scalene triangle that which has its three sides unequal"

"Euclid's Elements, Book I." Euclid's Elements, Book I. N.p., n.d. Web. 13 May 2015. <http://aleph0.clarku.edu/~djoyce/elements/bookI/bookI.html>.