jarak fokus cermin 2 cm. jarak benda terhadap cermin 3 cm, jarak bayangannya adalah ....

cermin apa? cekung apa cembung?
jenis cermin akan memengaruhi hasil perhitungan..

cermin cekung
s' = (sf)/(s - f)
s' = (3 × 2)/(3 - 2)
s' = 6/1
s' = 6 cm

cermin cembung
s' = (sf)/(s - f)
s' = (2 × -3)/(2 - (-3))
s' = -6/5 cm

f = 2 cm
s = 3 cm
s' = ...

1/f = 1/s + 1/s'
1/2 = 1/3 + 1/s'
1/s' = 1/2-1/3
1/s' = 3/6 - 2/6
1/s' = 1/6
s' = 6 cm