Grade 9 Mathematics: Angles Formed by Parallel Lines Cut by a Transversal

This set of vocabulary flashcards covers key terms and relationships regarding angles formed by transversals and parallel lines, as well as fundamental geometric angle pairs.

Transversal

A line, line segment, or ray that intersects two or more lines at different points.

Congruent Angles

Two angles that have the same degree measure, denoted by the symbol $\cong$, such that $\angle A \cong \angle B$ if $m\angle A = m\angle B$.

Complementary Angles

Two angles whose sum of their degree measures is $90$. They can be adjacent or nonadjacent.

Adjacent Angles

Two angles with a common vertex and a common side, but no common interior points.

Linear Pair

Two angles that are adjacent and their noncommon sides are opposite rays. Linear pairs are supplementary.

Supplementary Angles

Two angles whose sum of their degree measures is $180$. They can be adjacent or nonadjacent.

Vertical Angles

Angles formed by intersecting lines that are congruent, such as $\angle 1$ and $\angle 3$ or $\angle 2$ and $\angle 4$ in a cross-intersection.

Alternate Interior Angles

Nonadjacent angles that lie on opposite sides of the transversal and lie between the two lines; these angles are congruent.

Corresponding Angles

Angles that lie on the same side of the transversal and on the same side of the two lines; they occupy the same position at the two intersections and are congruent.

Alternate Exterior Angles

Angles that lie on opposite sides of the transversal and lie outside the two lines; these angles are congruent.

Same-Side (Consecutive) Exterior Angles

Angles that lie on the same side of the transversal and lie outside the two lines; these angles are supplementary and their sum is $180$.

Same-Side (Consecutive) Interior Angles

Angles that lie on the same side of the transversal and lie between the two lines; these angles are supplementary and their sum is $180$.