Two lines are each parallel to a third line. What is the relationship between the two lines?

When a transversal cuts two lines, **8 angles** are created (4 at each intersection). They are grouped into four pairs:

**Corresponding angles** — same position relative to each intersection (e.g., upper-left and upper-left).

**Alternate interior angles** — between the two lines, on opposite sides of the transversal.

**Alternate exterior angles** — outside the two lines, on opposite sides of the transversal.

**Co-interior (allied) angles** — between the two lines, on the SAME side of the transversal.

**If the two lines are parallel**:
- Corresponding angles are EQUAL.
- Alternate interior angles are EQUAL.
- Alternate exterior angles are EQUAL.
- Co-interior angles are SUPPLEMENTARY (sum 180°).