已知方程组4x-3y-6z=0,x+2y-7z=0(z≠0）,求x+y+3z/4x-y-5z的值

(1)×2得8x-6y-12x=0(3)(2)×3得3x+6y-21z=0 (4)(3)+(4)得11x-33z=0∴x=3z把x=3z代入(1)得12z-3y-6z=0∴6z-3y=0∴y=2z 把x=3z,y=2z代入x+y+3z/4x-y-5z得原式=(3z+2z+3z)/(12z-2z-5z) =8z/5z...