They are called “vertical angles.”
Vertical angles are angles formed by the same straight lines, but not adjacent to each other.
Read the other pair of vertical angles formed by the lines a b, c d.
Read all the vertical angles formed by the lines f g, i h. By l m, n p.
Why are the angles l o n, n o m adjacent angles?
Why are the angles l o n, p o m vertical angles?
Diagram 8.