若直线ax+2y-1=0与直线x-y+2=0平行,则实数a＝

题目

若直线ax+2y-1=0与直线x-y+2=0平行,则实数a＝

答案

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