Jawabanmu

2014-05-02T18:24:29+07:00
 \frac{1}{f}  \frac{1}{s}  \frac{1}{jarak bayangan}
 \frac{1}{20}  \frac{1}{30}  \frac{1}{jarak bayangan}
 -\frac{1}{jarak bayangan}  \frac{1}{30} -  \frac{1}{20}  \frac{-1}{60}
jarak bayangan = 60