已知，abc>0,求证，b+c/a+c+a/b+a+b/c大于等于6

(b+c)/a+(c+a)/b+(a+b)/c
=b/a + c/a + c/b + a/b + a/c + b/c
=( b/a + a/b ) + ( c/a + c/a) + (c/b+b/c)
>= 2 + 2 + 2
>=6