两点的中点为(-1/2 ,-1/2)
两点连线为 (y+1)/(x-1)=y/(x+2)
3y+x+2=0 斜率为-1/3
过中点(-1/2,-1/2)和3y+x+2垂直的直线即所求直线
所求直线斜率为3
(y+1/2)/(x+1/2)=3
y=3x+1