Question

a real image 1 divided 5 the size of object formed at a distance of 18 cm from a mirror what is the nature of the mirror calculate its focal length

Answer 1

m=-1/5=-v/u ..........(1)
v=-18cm ...............(2)
from1&2, we get,
u=18*5=90cm
then
1/v+1/u=1/f
-1/18+(-1/90)=1/f
f=-15cm
negative sign show mirror is concave