tolong dijawab no 29 & 30 terimakasih

29. dik: s = 20 cm
s' = 60 cm
dit: f =....?
jwb:
1/f = 1/s + 1/s'
= 1/20 + 1/60
= 30/60
f = 60/30
= 20 cm.
jadi, jarak fokus cermin tsb adalah 20 cm