Jawabanmu

2014-06-09T19:08:40+07:00
2/R = 1/So + 1/Si
2/R = 1/20 + 1/10
2/R = 1 + 2 / 20
2/R = 3/20
R/2 = 20/3
R/2 = 6,6
R = 6,6/2
R =  3,3 cm