6x²+xy-2y²+2x-8y-8 求：x的值 y的值

若x-y=6,xy=-8,求代数式(x+y+z)²+(x-y-z)(x-y+z)-2·z(x+y)的值 6x²+xy-2y²+2x-8y-8 求：x的值 y的值 已知x/y=2,求x²-xy+3y²/x²+xy+6y²的值 已知x-xy=8,xy-y=-9,求x+y-2xy的值 若正数x,y满足x²-y²=2xy,求（x-y)/(x+y)的值 正数x,y满足x²-y²=2xy,求x-y/x+y的值 已知x*x-4xy+4y*y=0 求[2x(x+y)-y(x+y)]/(4x*x-4xy+y*y)的值? 已知|x²-2xy-8y²|+2√x²-4xy+4y²-1=0,求3x+6y的值 4/X+1/Y=2,XY=-1,求代数式4Y-X/X-2Y/（x+2y-12Y²/x-2y)的值 已知xy²=-6,求xy(x^3y^7-3x^2y^5-11.5y)的值 已知x+y=4.x-y=6.求代数式xy(y²+y)-y²(xy+2x)-3xy的值 已知x/y等于3,求x²+2xy-3y²/x²-xy+y²的值