用柯西不等式证:(a/b+b/c+c/a)(b/a+c/b+a/c)≥9

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用柯西不等式证:(a/b+b/c+c/a)(b/a+c/b+a/c)≥9

(a/b+b/c+c/a)(b/a+c/b+a/c)
=((√a/b)^2+(√b/c)^2+(√c/a)^2)((√b/a)^2+(√c/b)^2+(√a/c)^2)
>=(√a/b*√b/a+√b/c*√c/b+√c/a*√a/c)^2
=(1+1+1)^2
=9