points a, b, and c form a triangle. complete the statements to prove that the sum of the interior angles of δabc is 180°.
statement reason
points a, b, and c form a triangle. given
let be a line passing through b and parallel to . definition of parallel lines
∠3 ≅ ∠5 and ∠1 ≅ ∠4
m∠1 = m∠4 and m∠3 = m∠5
m∠4 + m∠2 + m∠5 = 180° angle addition and definition of a straight line
m∠1 + m∠2 + m∠3 = 180° substitution