3x+4y+5z=0 (1)
2x+3y-4z=0 (2)
(1)-(2)
x+y+9z=0 (3)
x+y=-9z
(2)-2*(3)
y-22z=0
y=22z
代入(3)解得x=-31z
x-y=-53z
(x+y+z)/(x-y+z)
=(-9z+z)/(-53z+z)
=(-8)/(-52)
=2/13
3x+4y+5z=0 (1)
2x+3y-4z=0 (2)
(1)-(2)
x+y+9z=0 (3)
x+y=-9z
(2)-2*(3)
y-22z=0
y=22z
代入(3)解得x=-31z
x-y=-53z
(x+y+z)/(x-y+z)
=(-9z+z)/(-53z+z)
=(-8)/(-52)
=2/13