B В 4
5
Points A B, and Cform 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 B and parallel to AC. definition of parallel lines
23-25 and 21 44
m21 = m 24 and m2 3 = m 25
m24+ m2 2 + m 25 = 180°
angle addition and definition of a straight line
m 21 + m2 2 + m 43 = 180°
substitution