（2x+y-1)(2x-y+1)-(3x+y)(3x-y),其中x=5分之1,

x²/xy-x/y 3x/4x+y - x-2y/4x+y (1-y/y+x)÷x/y²-x² 若2/x-1/y=3,求[y/x-y/x-y(x-y/x-x+y)]/x-2y/x的值 化简 3x(x^2-x-1)-(x+1)(3x^-x) X^3(x-y)+x(y-x) (3x-y)^2+(3x+y)(3x-y),x=1,y=-2 二元一次方程 ：2(x+y)-(x-y)=3 (x+y)-2(x-y)=1 (x-y)/(x+y)=3求( 3x-2y-1)/(x+y-5) 2(x+y)-3(x-y)=1 6(x+y)+(x-y)=51 {3(x+y)-4(x-y)=4 {x+y/2 + x-y/6=1 变量x,y满足约束条件,x+y>=3,x-y>=-1,2x-y (Y-X)^3*(X-Y)^m+(X-Y) ^m+1*(Y-X)^2 (x-y)^2+(x+y)(x-y) 其中 X =3 Y=-1 [(-x-y)(-x+y)-(x+y)^2-x(y-y^2)}÷1/2y 1、(-7x^y)(2x^y-3xy^3+xy) 2、((x-y)^6)/((y-x)^3)/(x-y) x+y+2(-x-y+1)=3(1-y-x)-4-(y+x-1),x+y=? {(x+y)/2+(x-y)/3=1,(x+y)-5(x-y)=2.求x=?,y=? 1/(x-y)+1/(x+y)+2x/(x^2+y^2)+4x^3/(x^4+y^4)化简 1、y-x/x²-y²2、(x-y)(y-z)(z-x)/(z-y)(y-x)(x-z) (x/x+y-x/y-x-2xy/x.x-y.y)/(1/x-1/y) 分式化简