Theory:

Formation of image in a convex mirror:
  
In the following image, the ray \(OA\) parallel to the principal axis is reflected along with \(AD\). The ray \(OB\) retraces its path. The two reflected rays diverge, but they appear to intersect at \(I\) when produced backwards. Thus A1B1 is the image of the object \(AB\). It is virtual, erect and smaller than the object.
 
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A1B1 is the image of the object OO’
  
Uses of the convex mirror:
 
In automobiles, convex mirrors are used as rear-view mirrors. It creates a virtual, erect, small-scale image of the object every time. The size of the image grows as the vehicles approach the driver from behind. The image size decreases as the vehicles move away from the driver. In comparison to a plane mirror, a convex mirror has a much larger field of view.

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Rear-view mirror of a car
 
Convex mirrors are used as a traffic safety device on public roads. They are used on narrow roads with acute bends, such as hairpin bends in mountain passes, where oncoming vehicles cannot see you. It is also used in stores to cover blind spots.
 
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Convex mirror used in a supermarket
Reference:
https://www.pxfuel.com/en/free-photo-jrzpe
https://www.flickr.com/photos/centralasian/7131929699