Jawabanmu

2014-06-01T08:20:09+07:00
F=1/2r
 =1/2 x 20
 =10
1/f=1/h + 1/h'
1/10=1/5 + 1/h'
1/10 -1/5=1/h'
1/10 - 2/10 =1/h'
--1/10  = 1/h'
-10