For two or more lines, a transversal is any line which intersects two lines at distinct points. In the following figure, L1 and L2 are two lines which are cut at A and B by a transversal L0, resulting in a number of angles being formed:
There is a specific terminology associated with the angles formed when a transversal cuts two lines, as shown above. Let us quickly go over that terminology by taking the example of the figure above:
Corresponding angles
The following pairs of angles are corresponding angles:
- \(\angle 1\) and \(\angle 5\)
- \(\angle 2\) and \(\angle 6\)
- \(\angle 3\) and \(\angle 7\)
- \(\angle4\) and \(\angle 8\)
Alternate interior angles
The following pairs of angles are alternate interior angles:
- \(\angle 3\) and \(\angle 5\)
- \(\angle4\) and \(\angle 6\)
Alternate exterior angles
The following pairs of angles are alternate exterior angles:
- \(\angle 1\) and \(\angle 7\)
- \(\angle 2\) and \(\angle 8\)
Co-interior angles
The following pairs of angles are co-interior angles:
- \(\angle 3\) and \(\angle 6\)
- \(\angle4\) and \(\angle 5\)
We will now go on to the specific case of two parallel lines being cut by a transversal.