Question

已知4x-3y-6z=0，x+2y-7z=0，求5x+2y-z/2x-3y-10z的值

Answer 1

x+2y-7z=0 x=-2y+7z 2x=-4y+14z
由4x-3y-6z=0,x+2y-7z=0
得5x-y-13z=0 则5x=13z+y
所求5x+2y-z/2x-3y-10z=13z+y+2y-z/-4y+14z-3y-10z=12z+3y/-7y+4z
x=-2y+7z 5x=-10y+35z
又∵ 5x=13z+y
∴-10y+35z=13z+y
解得y=2z
5x+2y-z/2x-3y-10z=12z+3y/-7y+4z=18z/-10z=-9/5

Answer 2

4x-3y-6z=0 (1)
x+2y-7z=0 (2)
4(2)-(1)
11y-22z=0
y = 2z

from (2)
x+2y-7z=0
x+4z-7z=0
x= 3z

x:y:z = 3: 2 : 1
x=3k , y= 2k , z= k

(5x+2y-z)/(2x-3y-10z)
=(15k+4k-k)/(6k-6k-10k)
=18/(-10)
=-9/5