Jawabanmu

2014-05-05T10:59:54+07:00
P = 1/f
4 = 1/f
f = 0,25 m = 25 cm

1/f = 1/s benda + 1/s bayangan
1/25 = 1/s benda + 1/80
1/s benda = 1/25 - 1/80
1/s benda = 32/800 - 10/800
1/s benda = 22/800
s benda = 36,36 cm