∵x-2y+3z=0
∴ 3z=2y-x
z=(2y-x)/3
∵2x-3y+4z=0
∴ 4z=3y-2x
z=(3y-2x)/4
∴(2y-x)/3=(3y-2x)/4
4(2y-x)=3(3y-2x)
8y-4x=9y-6x
2x=y
∴x/y=1/2,y/x=2
∴（x的平方+3xy+2乘y的平方）除以2xy
=(x^2+3xy+2y^2)/2xy
=x^2/2xy+3xy/xy+2y^2/2xy
=x/2y+3+y/x
=1/4+3+2
=21/4