Verification: the sum of the internal angles of a triangle is equal to 180 ° and there must be a process of graph writing, verification and proof

Verification: the sum of the internal angles of a triangle is equal to 180 ° and there must be a process of graph writing, verification and proof

Known: triangle ABC proof: & lt; a + & lt; B + & lt; C = 180 ° prove: make a straight line through a point parallel to BC & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; by two straight lines parallel, the internal angle is equal & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; 1 = & lt; B & nbsp; & nbsp; & nbsp; & nbsp; {%