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{{ printedBook.courseTrack.name }} {{ printedBook.name }} If a pair of consecutive interior angles formed by a transversal are supplementary angles, the lines crossed are parallel lines.

For example, in the figure above the lines $A∣∣B$ because $α$ and $β$ is a pair of consecutive interior angles with an angle sum of $180_{∘},$ which makes them supplementary angles. The theorem is named the *Converse* Consecutive Interior Angles Theorem because the same thing holds true but in opposite order.