Answer:
opposite angles are congruent
Explanation:
thats because if you think about two intersecting lines and draw a circle around the angles you can imagine it as a circle (360 degrees) so whatever value the angles are they have to equal 360
so you may ask the question what does that have to do with anything? well i'm getting to that...the vertical angles are congruent because well one there is a theorem for it (search it up) and two it makes sense if you think of cutting a pizza all the way across and another line intersecting it all the way across. You notice how no matter how you position the two intersecting lines the angle opposite each other look the same. Thats because they are the same exact angle just directly across from each other. I hope this made sense :)