Points a, b, and c form a triangle. complete the statements to prove that the sum of the interior angles of sabc 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 = 24
m21 = m 24 and m23 = m25
m24+ m2 + m 25 = 180°
m21+ m2 2 + m23 = 180°
angle addition and definition of a straight line
substitution
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