已知（x+y）^2=9,(x-y)^2=5,求x^2+y^2和xy的值

已知x-y/x+y=3,求代数式5(x-y)/x+y-x+y/2(x-y) 已知x-y/x=x/x-2y（y不等于0）,求x：y的值 已知x-y=3,求[（x+y)(x-y)-(x-y)^2+2y(x-y)]除以的值 已知3x =2y 求x/x+y+y/x-y-y²/x²-y² x-y/x-x+y/y-(x+y)(x-y)/y² y/x=2 已知2x-y/x+2y=3,求2(2x-y)/x+2y-9(x+2y)/2x-y+3的值. 已知f(x+y,y/x)=x^2-y^2,则f(x,y)= 已知|x|=2,|y|=3,|x+y|=-(x+y)求x-y 已知x≠y,x^2-x=y^2-y,求x+y的值. 已知x>0,Y>0,如何证x^2/y+y^2/x>=x+y 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 已知方程组{(X+Y)-3(X-Y)=7,2(X+Y)+(X-Y）=-7}则(X+Y)(X-Y)= 已知X.x+y.y-4x+2y+5=0,求4X.X-12X Y+9Y.y的值 已知x+y=a,2x-y=-2a,求[（x/y-y/x)/(x+y)-x(1/x-1/y)]/[(x+1)/y]的值 已知x-2y=3,则(2x+y-6)/(3x-y-9)=? 已知x^2-y^2=45 x+y=9,求X-y的值 已知x^2-6xy+9y^2=0,求(x-y)/(x+y) 已知,X:Y=3:2,求代数式4X-9Y:2X+3Y