Triangle Angle Sum Theorem: A More Friendly Proof

Introduction

In high school mathematics, we were taught to write proofs in two columns. There are some proofs however that are easier to understand if we use Algebra. The triangle angle sum theorem that I have posted yesterday can be proven algebraically. Its proof which I think is easier to understand is shown below.

triangle angle sum

Theorem

The sum of the interior angles of a triangle is $latex 180^{\circ}$ Continue reading

The Triangle Angle Sum Theorem

Introduction

One of the most elementary concepts we have learned about triangles in Geometry is the angle sum theorem. The theorem states that the sum the three interior angles of a triangle is $latex 180^{o}$. We can easily see this by duplicating or cutting the corners of a triangle and meeting the angles at a particular point (see first figure). The adjacent angles will form a straight angle which is equal to $latex 180^{o}$.

trianlge angle sum

The proof of the angle sum theorem is quite easy. We just need to draw an extra line. Continue reading