y=x-7 3x-3y=21.y=x-73x-3y=21.

若(x-y)/(x+y)=3 则(x+2y)/(6x-7y)等于 计算3x/(x-3y)+(x+y)/(4y-x)-7y/(x-4y)=? 若x,y为正整数,且满足3x(x+y)-y(x+y)=7,求x,y 已知：2x+y=6,x-3y=1 求7y(x-3y)(x-3y)-2(3y-x)(3y-x) y=x-7 3x-3y=21.y=x-73x-3y=21. 7y(x-3y)-2(3y-x)=0 .x=?,y=? （x+y-5)*（x+y-5)+（x-y+3)=0 x*x-y*y 已知:3x-5y=0,求x/y,x-y/y,x-y/x 5(x-y)³-3（x-y）²+7(x-y)-5(x-y)³+（x-y）²-5（x-y）,其中,x-y=1/3.5(x-y)³-3（x-y）²+7(x-y)-5(x-y)³+（x-y）²-5（x-y）,其中,x-y=1/3先化简,再求值； 推倒公式:(x+y)(x*x-3x+y*y)=x*x*x+y*y*y怎么做. 若3x=7y,则y比x= ,x:（x+y）= 3x+5y-(x+y)=6 2(x+y)-3x=-7 已知方程组{(X+Y)-3(X-Y)=7,2(X+Y)+(X-Y）=-7}则(X+Y)(X-Y)= x+y=1 5x-2y=8 3x-y=7 2x-y=3x表示y和用y表示x x-y=3 7-x+y-y平方+X平方已知x-y=3 求代数式7-X+y-(y-x)²的值 已知（x+y）2 =2,(x-y)3 =3,求(x+y)7(x-y)2(x+y)3(y-x)4 的值 21/(x+y)+4/(x-y)=12/(x+y)+7/(x-y)结果为(x+y)/(x-y)=3求过程! 已知实数x.y满足根号(x+y-8)+根号(8-x-y)=根号(3x-y-4)+根号(x-2y+7),求x,y