{x+y=840;4x+8x+8y=4y+9y+9x帮我算一算,谢谢诸位了,我老是算错!

[(x+2y)(x-2y)-(x-2y)^2+8y(x+y)]除以4x= 4x+8(x+y)=840 4y+9(x+y)=840 (4x-2y-z)-{5x[8y-2y-(x+y)]-x+(3y-10z)]=? kuaihuajian 9y=3x-(x-1),4(x+y)-(2x+4)=8y [(2x-y)^2-y(y-4x)-8x]其中x=-1/2 若x-y=1 化简（x+y)(x^2+y^2)(x^4+y^4)(x^8+y^8)(x^16+y^16) [(2x+y)²-y(y+4x)-8x】/4x,其中x=-1,y=2005 急 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的平方+y的平方-8x+6y+25=0,求(x-y+4xy/x-y)(x+y-4xy/x+y) 已知x²+y²-8x+6y+25=0,求（x-y+4xy/x-y）（x+y-4xy/x+y） 已知x.x+y.y+8x+6y+25=0,求代数式(x.x-4y.y)/(x.x+4xy+4y.y)-x/(x+2y)的值 计算：(x-y)^8÷(y-x)^4×(x-y) {x+y=1 ,xy=-6{x(2x-3)=0,y=x²-1{(3x+4y-3)(3x+4y+3)=0,3x+2y=5{(x-y+2)(x+y)=0,x²+y²=8{(x+y)((x+y-1)=0,(x-y)(x-y-1)=0 (x-y) (x-2y)+(x+2y) (x-3y)-2(x-3y) (x-4y)= 因式分解：（x-2y)-4x+8y=4 X+Y=9 8X+4Y=56 x+8y=15 4x+y=29 x+y=16 8x+4y=104