Question

A concave lens has focal length of 15cm .If image at 10cm left from the lens, the object is placed at

Answer 1

u=?
v=10cm
f=15 cm

by 1/u+1/v=1/f

1/u=1/f-1/v
1/u=1/15 -1/10

1/u=-5/150
1/u= -1/30

u= -30 cm
u= 30 cm

Answer 2

F=15 cm
v= -10 cm
u=?
Then apply lens formula
1/f=1/v-1/u
u=-6cm