## Quick Reference

A straight line that intersects a given set of two or more straight lines in the plane. When a transversal intersects a given pair of lines, eight angles are formed; the four angles between the pair of lines are interior angles and the four others are exterior angles.

An interior angle between the transversal and one line and an exterior angle between the transversal and the other line, such that these two angles are on the same side of the transversal, are corresponding angles. An interior angle between the transversal and one line and an interior angle between the transversal and the other line, such that these two angles are on opposite sides of the transversal, are alternate angles. The given two lines are parallel if and only if corresponding angles are equal: they are also parallel if and only if alternate angles are equal.

The figure shows a transversal intersecting two lines. The angles *α* and *β* are corresponding angles and *α* and *γ* are alternate angles.

*Subjects:*
Mathematics.

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