Find the position of object which when placed in front of concave mirror of?

Find the position of object which when placed in front of concave mirror of


focal length 20cm produces a virtual image,which is twice the size of the object?Find the position of object which when placed in front of concave mirror of?
m= -v/u


so, 2= -v/u


u=-v/2





we know, 1/f =1/v +1/u ( f= -20cm, u=-v/2)


so, 1/-20=1/v + 1/-v/2


-1/20 = 1/v - 2/v


-1/20 = 1-2/v


-20=-v


so, v=20cm


so u= -10 cmFind the position of object which when placed in front of concave mirror of?
f = 20 cm


m = -v/u = 2


v = - 2u


Using mirror formula-


1/f = 1/v + 1/u


1/20 = 1/-2u + 1/u


u = 10 cm
Manu's ans is correct as f is negative because it is calculated in the opposite direction to the ray coming from the object.
between f and 2f