若直线ax+2y-1=0与直线x-y+2=0平行,则实数a＝
问题描述：
若直线ax+2y-1=0与直线x-y+2=0平行,则实数a＝
答
x-y+2=0,y = x+2,斜率1
ax+2y-1=0,y = -ax/2 +1/s,斜率:-a/2 = 1,a = -2