A Common Issue, Transervsal Angles
Transversals are defined as "A line that cuts across two or more (usually parallel) lines." (Source, mathopenref.com)
They are a bridge over water, there are two sides of the river (the parallel lines) and the bridge (transversal) cuts over the lines. Now, the transversal creates eight angles from the graph. Unless the transversal comes in at a 90 degree angle, there is usually two different angle subtypes: obtuse and acute.
If you know one of the angle measures, say 80 degrees, you can find the degree of the other angle by this formula:
180 - (Known Angle) = (Unknown Angle.
Or in our case,
180 - 80 = 100 degrees (which is the other angle)
So now we know that the two groups of angles are 80 degrees (acute) and 100 degrees (obtuse). All of the acute and obtuse will be 80 and 100, respectively.
There are a few more interesting things. We have alternate interior angles, alternate exterior angles, corresponding angles, and vertical angles.
Think of the bridge as a divider and the river as the "inside". Alternate interior angles are angles on the other side of the bridge and between both sides of the river. Alternate exterior angles are the angles on the other side of the bridge but outside the river. Corresponding angles are a little trickier. Say you were at the beginning and the end of the bridge. If you look to your left and see an angle at the beginning and the end of the bridge, you would be looking at the same angle that is a corresponding angle. And lastly and most easiest to understand are vertical angles; vertical angles are across from each other and they share know angle vectors. All of these angles are equivalent meaning if you have two angles are corresponding/vertical/alt. int./ alt. ext. they are the same angle measure.
Hope this clears up some issues with Geometry students! Have fun and happy mathings!