1.已知x^2-y^2=40,x+y=8/5,求x-y的.2.下列计算正确的是 （ ）A.(1/2+a)(-a+1/2)=a^2-1/4B.(-x-1)(x+1)=x^2-1C.-(x-a)(-x-a)=x^2-a^2D.(-a-9)(-9+a)=-81-a^23.(x-2y)^2=(x+2y)^2+A,则A等于 （ ）A.4xy B.-4xyC.8xy D.-8xy明天之前就要!

已知X*X+Y*Y+6X-8Y+25=0 求（Y/X)+(X/Y)-2=? 已知x+y/y=11/8,求x-y/x+2y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=11/8,求x-y/x+2y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 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^2+y^2-8x+12y+52=0 ,求1/2x-1/x-y(x-y/2x-x^2+y^2) 已知x^2+y^2-8x+12y+52=0 ,求1/2x-1/x-y(x-y/2x-x^2+y^2) 已知x-y=3,x+y=8,问x^2 -y^2=? 已知x^2+4y^2-4x+8y+8=0,求x+y 已知x+y=8,x-y=2,求x²+y²的值