Question

why do we prefer a convex as real view mirror in vehicle?

Answer 1

Thus, we require a mirror which gives us a wider view of the vehicles behind us. This is because a convex mirror forms a highly-diminished image, thus making the traffic look much smaller. As a result, we can see a large number of vehicles in a very smallmirror.

Answer 2

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. For example, the passenger-side rear view mirror on a car is convex.
hope it helps you