Question

assume that an object is kept at a distance of 20cm in front of a concave mirror its focal length is 30 cm then

Answer 1

Here,u=-20cm
f=-30cm
using mirror equation
1/f=1/v+1/u
1/v=1/f-1/u
=1/-30 +1/-20
=-1/12
f=-12 cm

Answer 2

Answer:

1/f=1/u+1/v

f=-30cm

u=-20cm

1/f=1/u+1/v

1/-30=1/-20+1/v

1/v=1/-30+1/-20

so - and - get cancel

then 1/v=1/30+1/20

lcm of 20 and 30 so it gets 60 so

2+3/60 =5/60

it gets cancel then you will get 12 so

answer v =12