​Do the 2 angles share a vertex?

If the 2 angles share a vertex, they are either vertical angles (across from each other) or they are a linear pair (together, they make a straight line). Vertical angles are congruent. Linear pairs are supplementary.

​What if the angles don't share a vertex?

If the 2 angles are in the same CORner, they are CORresponding angles.
As long as the lines are parallel, corresponding angles are congruent.

​If the 2 angles don't share a vertex
and aren't corresponding . . .

Are they on the SAME SIDE of the transversal or are they on ALTERNATE SIDES?

​If both angles are on the same side
of the transversal, they're either
Same-Side Interior or Same-Side Exterior angles.

​Either way, as long as the lines are parallel, the angles are supplementary.

​​If both angles are on opposite sides
of the transversal, they're either
Alternate Interior or Alternate Exterior angles.

​Either way, as long as the lines are parallel, the angles are congruent.

You can write and solve equations based on the type of special angle pair.

• If the angles are congruent,

  set them equal to each other.

• If they're supplementary,

  they add up to 180.