Vertically Opposite Angles: When two lines intersect, they form two pairs of opposite angles. Vertically opposite angles are always equal.

Adjacent Angles: When two angles are adjacent and form a straight line, they add up to 180°. This makes them supplementary angles.

Parallel Lines and Transversals: When a transversal intersects parallel lines, it creates corresponding, alternate, and co-interior angles, a common topic in geometry.

Co-Interior Angles: Co-interior angles lie on the same side of the transversal and sum up to 180 degrees.