Jawabanmu

2014-06-11T14:11:29+07:00
1/s1=1/12 -1/8
1/s1=2/24 -3/24
s1= 24cm
2014-06-11T14:14:52+07:00
1/f = 1/s + 1/si 
1/12 = 1/8 + 1/si
1/12 - 1/8 = 1/si
2/24 - 3/24 = 1/si 
-1/24 = 1/si 
si = -24 (terletak diblakan cermin)