∵2ax-by+2=0(a>b>0)始终平分圆x^2+y^2+2x-4y+1=0的周长∴直线2ax-by+2=0必经过圆心（-1,2）∴-2a-2b+2=0∴a+b=1∵(a>b>0)∴（a-b）²＞0∴a²+b²＞2ab∴a²+b²+2ab＞3ab即（a+b）²＞3ab∴ab＜1/31/a+1/b=(a+b)/ab=1/ab＞3
