An obect is placed 20cm from a convex mirror of focal length 12cm. where does the image form?

7.5 cm behind the mirror

Explanation:

Applying,

Using the real is positive convection: All real distance from the mirror are positive

1/f = 1/v+1/u Equation 1

Where f = focal length of the mirror, v = image distance, u = object distance

From the question,

f = -12 cm, u = 20 cm

substitute these value into equation 1

1/(-12) = (1/20)+1/v

(-1/12)-(1/20) = 1/v

1/v = (-5-3)/60

1/v = -8/60

v = -60/8

v = -7.5 cm

Hence the image is formed 7.5 cm behind the mirror.