Question 457435
{{{drawing(300,300,0,10,0,10,


triangle(2,2,8,2,3.5,7),
line(2,7,8,7),
locate(2.5,2.5,A),
locate(3.5,7,B),
locate(7.5,2.5,C),
locate(2.5,7,A),
locate(4.5,7,C)


)
}}}


Given the triangle with angles A,B,C we can draw a line through one vertex that is parallel to the base. Because the two lines are parallel, we can label the remaining angles A and C. Here it is clear that A+B+C = 180 since A,B, and C form a straight angle.