Thales, the Greek mathematician from Miletus, Ionia (today’s Western Turkey), is credited for formulating the very first “Principles of Geometry.”

Imagine, although human beings were alive on earth for hundreds of thousands of years, they had to wait until 6th century B.C. to find out the following interesting rules that guide the behavior of triangles and circles:

Thales’ Rule No. 1: If you draw any triangle inside a circle, if the tip of the triangle is resting on the circumference and the diameter of the circle is forming the long side of the triangle, then the angle formed by the other two shorter sides forms a 90 degree right angle – regardless of the length of the shorter sides. (This rule is also commonly known as “Thales’ Theorem.”)

Thales’ Rule No. 2: The diameter of any circle bisects it into two equal parts and into two arcs of equal lengths.

Thales’ Rule No. 3: If two triangles have one side that is of equal length and two angles that are of equal degrees, then those two triangles are identical.

Thales’ Rule No. 4: Two straight lines crossing each other form four angles around their intersection point. The angles opposing one another are equal angles. That is, two intersecting straight lines form two pairs of equal angles.

Thales’ Rule No. 5: A triangle with two equal sides, i.e., an isosceles triangle, have equal angles where the equal sides intersect with the third side.

We owe the beginnings of our modern-day mathematics and geometry to a man who was so in love with what he is doing that one day, according to Plato, Thales fell into a water well while gazing at the stars. Thus perhaps it won’t be too much off the mark to say that Thales was also the very first “absent minded professor” we had.