a+2b=3那么1 = a/3 + 2b/31/a + 1/b=(a/3+2b/3)/a + (a/3+2b/3)/b=1/3 + 2b/3a + a/3b + 2/3=1 + 2b/3a + a/3b对于后面带a,b的两项运用基本不等式即可2b/3a = a/3b 时可以取得最小值之后的过程就自己算吧...