若(x+y-7)^2+|x^2-y^2-56|=0,则x-y的值为________

若(x-y)/(x+y)=3 则(x+2y)/(6x-7y)等于 x-y/x-x+y/y-(x+y)(x-y)/y² y/x=2 化简y(x+y)+(x+y)(x-y)-x^2 化简3(x-y)-7(x--y)+2(y-x) (x+y)(x-y)-(x-y)^2如题 (x+y)(x-y)-(x-y)^2 【2(x-y)(x-y)(x-y)-8(x-y)(x-y)(x+y)+6y(x-y)(x-y)]/2(x-y)(x-y) 因式分解x(x+y)(x-y)-x(x+y)^2 [(x-y)^2-(x+2y)(x-2y)]/y 计算:y-x分之x+y+x-y分之y-y-x分之2x-y 若2/x-1/y=3,求[y/x-y/x-y(x-y/x-x+y)]/x-2y/x的值 [(x+2y)²-(x+y)(x-y)-7y²】÷（2y） x^2(x-y)+(y-x) x(x-y)2-(y-x)3 【(x-y)^2+(x+y)(x-y)】除以 2x [(x-y)²+(x+y)(x-y)]除以2x x+2y=2x+y+1=7x-y 求：2x-y? 解方程组(x+y)(x-2y)=-5 (x-y)(x+2y)=7 (x-y)^2+7(x+y)-11(x-y)^2-8(x+y),先化简.再求值