Question

prove that sum of all the angles of a triangle is 180degree.

Answer 1

draw a line parallel to any side of the triangle but passing through the opposite vertex
now the other two angles become alternate interior angles of the triangle. It can be clearly seen that the three Angles form a linear pair

Answer 2

as the triangle has three sides,

here, used formula = (2n-4) *90            [  n is denoted to number of sides]

then , in triangle,

[(2*3) -4]*90

(6-4)*90

2*90

180

hence proved that the sum of angles of triangle is 180