1)a+b+c=1≥3(abc)^1/3 abc≤1/27 1/abc≥27 (1/a+1)(1/b+1)(1/c+1) =1/a+1/b+1/c+1/ab+1/bc+1/ac+1+1/abc≥3(1/abc)^1/3+3 (1/abc)^2/3+1/abc+1=64 >=1000/27
