two intersecting lines create four angles with the same vertex, labeled A,B,C,and D

Answer 1

When two intersecting lines create four angles with the same vertex, they form a shape called a cross or a plus sign (+). The angles created are labeled A, B, C, and D.

An illustration of this can be seen below:

B
|
C----+-----D
|
A

In this case, angle A is opposite angle C, and angle B is opposite angle D. These pairs of angles are called vertical angles and are always congruent (i.e. they have the same measure).