Lines Angles and Triangles Theorem 5

Statement

The sum of the three angles of a triangle is 180^o.

Given:

A triangle MNS.

To prove:

Construction:

Proof:

MN is a transversal.

(Alternate angles)

.

. …(2) (Alternate angles)

From the figure,

( is a straight line and sum of the angles at M = 180^o)

From (1) and (2),

Thus it is proved that sum of the measures of the three angles of a triangle is equal to 180^o or two right angles.