(2/x+1/y)(x+y)=2+1+2y/x+x/y由基本不等式有2y/x+x/y≥2√(2y/x*x/y)=2√2所以2/x+1/y=(2/x+1/y)(x+y)=2+1+2y/x+x/y≥3+2√2当x=2-√2,y=√2-1时取到
