D B
E
4
5
41
с
Points A, B, and form a triangle. Complete the statements to prove that the sum of the Interior angles of AABC IS 180°.
Statement
Reason
Points A, B, and C form a triangle.
given
Let DE be a line passing through Band parallel to AC. definition of parallel lines
23 =25 and 21 = 24
m21 = m 24 and 23 = m 25
m24+ m2 2 + m 25 = 180°
m21 + m2 + m23 = 180°
angle addition and definition of a straight line
substitution