∵圆的方程是x^2+y^2+2x-4y+1=0,即(x+1)^2+(y-2)^2=4∴圆心是(-1,2),半径长是2∵直线截得的弦长为4,正好是直径长∴直线2ax-by+2=0过圆心(-1,2)∴a+b=1∴1/a+3/b=(1/a+3/b)×1=(1/a+3/b)(a+b)=4+b/a+3a/b≥4+2√[(b/a...