x+y+z=0,.(1)
5x-3y-z=0.(2)
(1)+(2),得
6x-2y=0
2y=6x
y=3x
代入(1),得
x+3x+z=0
z=-4x
所以
5x-y+z/2x+8y+7z
=(5x-3x-4x)/(2x+24x-28x)
=(-2x)/(-2x)
=1