Lines Angles and Triangles


   
 
Theorem 5
Statement
 
The sum of the three angles of a triangle is 180o.
 
 
 
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 = 180o)
 
From (1) and (2),
 
 
Thus it is proved that sum of the measures of the three angles of a triangle is equal to 180o or two right angles.
 
 
     
   
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