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A transversal t intersects two parallel lines a and b, and forms two groups of angles. On top line a, starting from the top left, clockwise, angles are 1, 2, 3, and 4. On below line b, starting from the top left, clockwise, angles are 5, 6, 7, and 8.

In the figure,
a
∥
b
, and both lines are intersected by transversal t. Complete the statements to prove that ∠2 and ∠8 are supplementary angles.


a
∥
b
(given)
m∠2 = m∠7 ()
m∠7 + m∠8 = 180° ()
m∠2 + m∠8 = 180° (Substitution Property)
∠2 and ∠8 are supplementary (definition of supplementary angles)