Theory:

Rules for the construction of image by a Concave mirror:

We need to know the following rules to find the position and nature of the image formed by a spherical mirror.
 
Rule 1:
 
A ray passing through the centre of curvature is reflected along its path.
 
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A ray passing through the centre of curvature
  
Rule 2:
 
A ray parallel to the principal axis passes through or appears to be coming from the principal focus after reflection.

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Ray parallel to the principal axis
  
Rule 3:
 
A ray passing through the focus gets reflected and travels parallel to the principal axis.

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Ray travelling through the principal focus
  
Rule 4:
 
A ray incident at the pole of the mirror gets reflected along a path such that the angle of incidence is equal to the angle of reflection.
 
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The angle of incidence is equal to the angle of reflection