Jawabanmu

2014-05-25T17:10:23+07:00
Fokus lensa cekung selalu negatif maka f= -20
s= 30 cm
s' = ?
1/s + 1/s' = 1/f
1/30 + 1/s' = -1/20
1/s' = -1/20 - 1/30
1/s' = -1/60
s' = -60 cm