Jawabanmu

2014-08-10T23:57:46+07:00
(x + y)^-1 / (x^-1 + y^-1)
= (x + y)^-1 / { (x + y) / xy }
= (x + y)^-1 *  (x + y)^-1 * xy
= xy * (x + y)^-2
ato = xy / (x + y)^2