y+1=kz,3+1=2k,k=2
z=m(x-1),-4=m(3-1),m=-2
所以
y+1=2z .(1)
z=-2(x-1) .(2)
将(2)代入(1):y+1=2*(-2)(x-1)
y=-4(x-1)-1
y=-4x+3