Prove that sum of all of interiors angle of triangle is 180°

1.	Prove that sum of all of interiors angle of triangle is 180°
Answer» In ∆ ABC, const. a line PQ through point A and parllel to BC. Then angle PAB + angle A + angle QAC=180° BUT angle PAB=angle B and Angle QAC=angle C [ alternative int. angle] SO, angle B + angle A + angle C = 180° ∆ABCangle A +angle B +angle C =180° (angle sum property of a triangle)

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