Question

prove that sum of interior angles of triangle is 180 degrees

Answer 1

DRAW A LINE AT THE TOP OF TRIANGLE BY THIS 3 ANGLE X,Y,Z=180 BECAUSE THEY ARE IN STRAIGHT LINE THEN X&Y ARE VERTICALLY OPPOSITE TO OTHER 2 CORNERS OF TRIANGLE AND Y IS CONSTANT IN ITS PLACE
BY THIS  
X+Y+Z=180

Answer 2

by exterior angle property 
extend bc so new angle formed ang.4
ang. 1 + ang. 2 = ang. 4 
ang. 4 + ang 3= 180
add both the eq.
ang 1 + 2+3 =180