向量AB=向量CD
(-4,-2)=(x+3,3-y)
x+3=-4
3-y=-2
x=-7,y=5.
设P坐标是(m,n),C(-7,3),D(-3,5)
m=(-7+1/3*(-3))/(1+1/3)=-6
n=(3+1/3*5)/(1+1/3)=3.5