Question

To construct ray diagrams , two rays of light are generally so chosen that it is easy to determine their direction after reflection from a mirror. Chose two such rays and state the path of these rays after reflection from a concave mirror , Use these two rays to find the position and nature of the image of an object placed at a distance of 8cm from a concave mirror of focal length 12cm

Answer 1

1/f = 1/v + 1/u = -1/12 = 1/v - 1/8 
v = 24 c.m
 image is formed behind the mirror n is virtual and erect  because image distance is positive. 
also , m= -v/u = 3
hence this also shows that image is erect n virtual 

Answer 2

see chose the rays one which is parallel to the radius of curvature and other from the center of the mirror

as the distance of object is less than focal length the image will be a virtual one

1/f = 1/u + 1/v

1/-12 = 1/-8 + 1/v

1/v = 1/8 - 1/12

1/v = 1/24 

v = 24 cm