Parallel Lines & Transversals Flashcards

When two parallel lines are cut by a transversal, alternate interior angles are _____.

Answer: equal

Alternate interior angles are congruent (equal) when the lines cut by the transversal are parallel.

Co-interior angles (same-side interior angles) formed by two parallel lines and a transversal sum to _____.

Answer: 180°

Co-interior (consecutive interior) angles are supplementary, always summing to 180° when the lines are parallel.

Corresponding angles formed when a transversal cuts two parallel lines are _____.

Answer: congruent

Corresponding angles occupy the same relative position at each intersection and are equal when lines are parallel.

When a transversal intersects two parallel lines, how many pairs of corresponding angles are formed?

Answer: 4

The transversal creates 4 angles at each of the 2 intersections (8 angles total), forming exactly 4 pairs of corresponding angles.

If one co-interior angle measures 115°, what is the other co-interior angle when the lines are parallel?

Answer: 65°

Co-interior angles sum to 180°, so the other angle is 180° − 115° = 65°.

Alternate exterior angles are located _____.

Answer: outside the parallel lines on opposite sides of the transversal

Alternate exterior angles are on opposite sides of the transversal and exterior (outside) to the two parallel lines.

If a transversal cuts two lines and the alternate interior angles are NOT equal, then the two lines are _____.

Answer: not parallel

Alternate interior angles are equal only when the lines are parallel; unequal alternate interior angles indicate the lines are not parallel.