Corresponding angles
The corresponding angles definition tells us that when two parallel lines are intersected by a third one (transversal), the angles that occupy the same relative position at each intersection are known to be corresponding angles to each other.
Why is Line 1 = Line 2 ?
Well corresponding lines are only possible when lines are parallel and they have a transversal intersecting them
Both of the angles have a initial position in the diagram which makes them have the same angles
If the lines are not parallel or if there is no transversal then the corresponding angle theory wont match
Some corrections are there, discuss with me