Apabila cermin cekung fokus nya 3cm dan jarak benda 12cm.tentukan jarak bayangan

1/f = 1/s + 1/s'
1/3 = 1/12 + 1/s'
1/s' = 1/3 - 1/12
1/s' = 4/12 - 1/12
1/s' = 3/12
s'= 12/3 = 4 cm

Maaf kalau salah:))