tolong bantuin ya, fisika bab optik

Keadaan pertama
s = 20 cm
s' = 40 cm

jarak fokus lensa
f = s s' / (s + s')
f = 20 • 40 / (20 + 40)
f = 40/3 cm


Keadaan kedua

jarak fokus lensa gabungan
fg = f /2
fg = (40/3) / 2
fg = 20/3 cm

s = 20 cm

jarak bayangan
s' = s fg / (s - fg)
s' = 20 • 20/3 / (20 - 20/3)
s' = 400/3 / (40/3)
s' = 10 cm ← hwb