设点(x,y)是所求直线上一点,则点(x,y)关于直线x+y=0对称的点(-y,-x)
在直线x-2y+3=0上,所以:-y-2(-x)+3=0,化简:2x-y+3=0,
故:所求直线方程是:2x-y+3=0