1/a+2/b=(1/a+2/b)*1=(1/a+2/b)(a+b)=1+2+b/a+2a/b=3+b/a+2a/ba>0,b>0由均值不等式b/a+2a/b>=2√(b/a*2a/b)=2√2当b/a=2a/b相等b^2=2a^2b=√2aa+b=1,有符合a>0,b>0的解所以可以取等号所以1/a+2/b>=3+2√2所以最小值=3+2√2
