Mathematics

Proving Alternate Interior Angles are Congruent (the same)

The Alternate Interior Angles Theorem states that If two parallel straight lines are intersected by a third straight line (transversal), then the angles inside (between) the parallel lines, on opposite sides of the transversal are congruent (identical). This is illustrated in the image below: We see two parallel lines and a third line (transversal) intersecting […]

Mathematics

Proving that the Angles in a Triangle Sum up to 180°

Proving that the angles inside a triangle – any triangle – sum up to 180° is very simple, but leaves most people unsatisfied (or unconvinced) because it depends on the properties of something called Alternate Interior Angles. I’ll give the proof first and then explain Alternate Interior Angles A demonstration of the angles of a […]