Question

prove that an exterior angle of a triangle is equal to the sum of its interior angle
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Answer 1

let's take a example :

exterior angle =135°

angle sum property of triangle =180°

adjacent angle of exterior angle =180-135=45°

now subtract 45 from 180 ( 45 is adjacent angle of exterior angle and 180 is sum of all angles of triangle )  

you will find the sum of two angles opposite to adjacent angle

180-45=135°  

∴ exterior angle and and two opposite angles of adjacent angle is equal  

Answer 2

Answer:

hence proved an exterior angle of a triangle is equal to the sum of its interior angle