设所求对称点为(a,b)直线2x-y+1=0斜率为k1=2过点(1,-2) ;(a,b)的直线斜率为k2=(b+2)/(a-1)k1*k2=-1即2(b+2)/(a-1)=-1 ①两点连线的中点坐标为[(a+1)/2,(b-1)/2]中点坐标在直线2x-y+1=0上所以2*(a+1)/2-(b-1)/2+1=0 ...