SOLUTION: why do the interior angles of a triangle add up to 180 ?

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Question 457435: why do the interior angles of a triangle add up to 180 ?
Found 2 solutions by MathLover1, richard1234:
Answer by MathLover1(20849) About Me  (Show Source):
You can put this solution on YOUR website!

take a triangle and draw a line thru one vertex that is parallel to the base
now since these are opposite angles,they are equal
so, if A is the angle of the triangle at the vertex, the rest two along the line will be B and C

since the angle at a point on the straight line is 180, sum of angles in a triangle is 180

Answer by richard1234(7193) About Me  (Show Source):
You can put this solution on YOUR website!


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.