opposite rays have common end points
Is it true
no. A segment is a line with end points. Rays start in one place and go on forever.
An angle
if the rays have no common points, the answer is zero. if the rays all have the same end point, the answer is 21 -- counting only the acute angles.
Yes, the definition of an angle is The amount of turn between two straight lines that have a common end point (the vertex). You can think of the arms as the two rays.
Gamma rays are at the end of the spectrum
Two collinear rays with the same endpoint form an angle. They share a common initial point and extend in opposite directions. The endpoint where they meet is called the vertex of the angle.
They are at the end points of its diagonals
angle
An angle is formed between the two rays at the common end point.
Two and only two rays having the same end points are in an angle.