2x-y+z=0 3x+8y-z=0 且xyz不等于0,求(2x²-xy+z²)/(2x²+y²-z²)的值

2x-y+z=0 3x+8y-z=0两式相加得 5x + 7y = 0x/y = - 7/5x = - 7/5 y 代入 2x - y+z = 0 得- 14/5 y - y + z = 0z/y = 19/5(2x²-xy+z²)/(2x²+y²-z²)分子分母同除以 y²= [ 2(x/y)² ...