Geometry: Angle Theorems

Corresponding Angles Postulate : If two parallel lines are crossed by a transversal, then the pairs of corresponding angles are always congruent.

Converse of Corresponding Angles Postulate : If any two lines are crossed by a transversal and the corresponding angles are congruent, then the two lines are parallel.

Same-side Interior Angles Theorem : If two parallel lines are crossed by a transversal, then each pair of same-side interior angles is supplementary.

Converse of Same Side Interior Angles Theorem : If two coplanar lines are crossed by a transversal so that a pair of same-side interior angles is supplementary, then the two lines are parallel.