Question

prove that the sum of three angles are 180 degree​

Answer 1

Answer:

To prove the above property of triangles, draw a line \overleftrightarrow {PQ} parallel to the side BC of the given triangle. Thus, the sum of the interior angles of a triangle is 180°.

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Answer 2

$\huge\colorbox{green}{Answer}$

Angles B and B' are corresponding angles, ... So, the angle sum ∠A + ∠B + ∠C is equal to the angle sum ∠A' + ∠B' + ∠C'. The three angles A', B', and C' form together a straight angle (they are along the line l). So, their angle sum is 180°.