Is concave mirror also used in car side mirror?

Yes!!ofcourse the concave mirrors are used in the rear mirrors of cars.

thats why it is written in most the objects in the mirrors are closer than they appear. moreover the work of concave mirror is that the light rays which are coming in parallel are concentrated to the same parallel incident ray but this line are such thrown back away that they concentrate a point and intersect and is called for "focus".this helps in zooming object.