4X—3Y—6Z=0 X+2Y—7Z=O（XYZ不等于0）求代数式X-y+z除以x+y+z的值

题目

4X—3Y—6Z=0 X+2Y—7Z=O（XYZ不等于0）求代数式X-y+z除以x+y+z的值

答案

先把z当作常量,则原方程化为4x-3y=6z,x+2y=7z,解此方程组得x=3z,y=2z,
故(x-y+z)/(x+y+z)=(3z-2z+z)/(3z+2z+z)=1/3