柯西不等式：[1/(1-a)+1/(1-b)+1/(1-c)][(1-a)+(1-b)+(1-c)]≥9 则 1/(1-a)+1/(1-b)+1/(1-c)≥9/[3-(a+b+c)] 而 2(a+b+c)^2=(a^2+b^2)+(a^2+c^2)+(b^2+c^2)+4ab+4ac+4bc ≥2ab+2ac+2bc+4ab+4ac+4bc=6(ab+ac+bc)=6 所...