(a＋b－c)／c＝(a－b＋c)／b＝(－a＋b＋c)／a
(a＋b+c-2c)／c＝(a+b＋c-2b)／b＝(a＋b＋c-2a)／a
(a＋b+c)／c-2＝(a+b＋c)／b-2＝(a＋b＋c)／a-2
(a＋b+c)／c=(a＋b+c)／b=(a＋b+c)／a
a=b=c
x=2a*2b*2c/abc=8