Jawabanmu

2014-05-29T19:47:01+07:00
1/f = 1/so + 1/si
     = 1/20 - 1/10
     =  \frac{1-2}{20}
1/f  = -1/20
-f   = 20
f    = -20 
jarak fokus = -20 cm
si min karena cermin cembung