Question

why does the driver uses concave mirror instead of plane mirror as a rear view mirror?????

Answer 1

Because the image is smaller, more image can fit onto the mirror, so a convex mirror provides for a larger field of view than a plane mirror. This is why they are useful. They are used whenever a mirror with a large field of view is needed.

Answer 2

this is because it gives virtual erect and diminished image of the object and provides a wide range of view to the driver