Suatu benda berada 15cm di depan cermin cembung yang berjari jari 20cm. Jika tinggi benda 3 cm,tinggi bayangan yg dihasilakn?

s = 15 cm, R = -20 cm dan h = 3 cm
f = R / 2 = -20 cm / 2 = -10 cm

1 / f = 1 / s + 1 / s'
s' = sf / (s - f)
   = (15 cm)(-10 cm) / (15 cm + 10 cm) = -6 cm

M = -s' / s = h' / h
h' = -hs' / s
   = -(3 cm)(-6 cm) / (15 cm) = 1,2 cm