倾斜角互补则斜率是相反数
所以(y1-2)/(x1-1)=-(y2-2)/(x2-1)
x1=y1²/4,x2=y2²/4
所以(y1-2)/(y1²/4-1)=-(y2-2)/(y2²/4-1)
4(y1-2)/(y1+2)(y1-2)=-4(y2-2)/(y2+2)(y2-2)
1/(y1+2)=-1/(y2+2)
y2+2=-y1-2
y1+y2=-4
k=(y2-y1)/(x2-x1)
=(y2-y1)/(y2²/4-y1²/4)
=4(y2-y1)/(y2-y1)(y2+y1)
=4/(y2+y1)
=4/(-4)
=-1