Jawabanmu

2014-05-23T08:57:35+07:00
1/f = 1/s + 1/s'
1/8 = 1/4 + 1/s'
1/s' = 1/8 - 1/4
1/s' = -1/8
s' = -8 (Insyaalloh)
2014-05-23T09:10:22+07:00
Diket: s= 4 cm
          f= 8 cm
         s'= . . . ?
1/f = 1/s + 1/s'
1/s' = 1/f - 1/s
      = 1/8 - 1/4
      = (1 - 2) /8
1/s' = -1/8
s' = -8 cm