Question

Diverging lens of focal length 15cm forms image of distance 10cm from lens. How far is the object placed from lens?

Answer 1

since diverging lens is concave lens so its focal length will be negative
f= -15 cm  v=-10 cm 
now 1/f= 1/v-1/u
1/-15=1/-10 - 1/u
1/-15+1/10= -1/u
u= -30 cm