已知实数x>0,y

由y=(2-2x)/(x+1)=4/(x+1)-2=4/3,x>=1/3
z=2x+y=2x+4/(x+1)-2=2(x+1)+4/(x+1)-4>=2√8-2=4√2-2
当2(x+1)=4/(x+1),x+1=√2,x=√2-1时取最小值4√2-2