(1/a-1)(1/b-1)(1/c-1)=( a+b+c/a-1)(a+b+c/b-1)(a+b+c/c-1) =(1+b/a+c/a-1)(a/b+1+c/b-1)(a/c+b/c+1-1) =(b/a+c/a)(a/b+c/b)(a/c+b/c) >=2根号bc/a2*2根号ac/b2*2根号ab/c2 =8