An angle.
A vertex is the common endpoint of two rays. Vertex typically means a corner or a point where lines meet. For example a square has four corners, each is called a vertex.
No, its an angle, not a vertex. I promis:)
angle
Octagon
poop
angle
angle
An angle.
An angle
A right angle (90 degrees).
an angle
Angle
a rainbow 
Yes. Any two rays which have the same end point.
An angle.
A line
angle
an angle
Angle
An angle.
angle
an acute ray