向量AB=（6,1）,向量BC=（x,y）向量CD=（-2,-3）,且BC‖AD.（1）求x与y间的关系；

AB=(6,1),BC=(x,y),CD=(-2,-3)
BC//AD
AD = AB+BC+CD
=( 4+x,-2+y)
BC//AD
=> y/x = (-2+y)/(4+x)
y(4+x)= x(-2+y)
4y+xy = -2x+xy
4y = -2x
x = -2y