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If two parallel lines are cut by a transversal, then the pairs of corresponding angles...

are congruent

If two parallel lines are cut by a transversal, then the pairs of alternate interior angles...

are congruent.

If two parallel lines are cut by a transversal, then the two pairs of alternate exterior angles...

are congruent.

If two parallel lines are cut by a transversal, then the two pairs of same side interior angles...

are supplementary.

If two coplanar lines are cut by a transversal so that the corresponding angles are congruent, then...

the two lines are parallel.

Through a point P not on line l, there is...

exactly one line parallel to l.

If two coplanar lines are cut by a transversal so that the alternate interior angles are congruent, then...

the two lines are parallel.

If two coplanar lines are cut by a transversal so that the alternate exterior angles are congruent, then...

the two lines are parallel.

If two coplanar lines are cut by a transversal so that the same side interior angles are supplementary, then...

the two lines are parallel.

If two intersecting lines form¬¬-__________, then the lines are perpendicular.

a linear pair of congruent angles

In a plane, if a transversal is perpendicular to one of two parallel lines, then...

it is perpendicular to the other line.

If two coplanar lines are perpendicular to the same line, then...

the two lines are parallel to each other.

In a coordinate plane, two nonvertical lines are parallel if and only if...

they have the same slope. (Any two vertical lines are parallel.)

In a coordinate plane, two nonvertical lines are perpendicular if and only if...

the product of their slopes is -1. (Vertical and horizontal lines are perpendicular.)