# How to prove the sum of angles in a Triangle is 180°

We Know sum of angles in a tri angle is 180° but how can we prove that Consider triangle ABC

Draw a line which is parallel to “AB” and passing through “C”

Their is new angles ∠ACD and ∠BCE are formed

So from figure we understand that

∠ACD = ∠A Alternate intern angles

∠BCE = ∠B Alternate intern angles

So

Sum of angles of

triangle = ∠A+∠B+∠ACB

= ∠ACD+∠BCE+∠ACB

= 180° because

DE is a straight line

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