法二先证得1/a2+1/b2+1/c2≥1/ab+1/ac+1/bc而(1/a+1/b+1/c)^2=1/a2+1/b2+1/c2+2(1/ab+1/ac+1/bc)≥3(1/ab+1/ac+1/bc)3就是这么来的.答案最后用的不等式实际是三个基本不等式的叠加ab+3/ab≥2根号3ac+3/ac≥2根号3bc+...