Draw a figure and then look at both these terms.
have you ever seen rays of light or sunlight?
Recall the realtion bwteen radius of curvature and focal length.
Think about both the spherical mirors.
These images can also be seen at cinema halls.
Which mirror has bulging-out surface?
Recall the realtion bwteen radius of curvature and focal length.
At which point parallel rays converges?
Recall the laws of reflection.