一道数学题，帮帮忙~~~~~~

x-3y+z=0
3x-3y-4z=0

相减得 -2x+5z=0
z=2x/5
代入第一式得
y=7x/15
((2x+6y-11z)/(4x-12y+z))^2
=[(2+6*7/15-11*2/5)/(4-12*7/15+2/5)]^2
=[(30+42-66)/(60-84+6)]^2
=1/9

联立前两个等式可解得x=5z/2,y=7z/6并带入
((2x+6y-11z)/(4x-12y+z))^2，最后会约掉z算出值