题如下,
因为2x+y=1,所以1/x+1/y=(1/x+1/y)(2x+y)=2+1+y/x+2x/y=3+y/x+2x/y而由均值不等式:y/x+2x/y≥2√[(y/x)×(2x/y)]=2√2,所以1/x+1/y=3+y/x+2x/y≥3+2√2
