X+4=Y-8,而且x+y=40,x=?,y=?

(x+y)(x+2y)(x+3y)(x+4y)=-40 [(x+2y)(x-2y)-(x-2y)^2+8y(x+y)]除以4x= 【2(x-y)^3-8(x-y)^2(x+y)+6y(x-y)^2】/2(x-y)^2= x y是两个变量,而且x=4/y.请先填表,再判断x和y是什么比例 (4x-2y-z)-{5x[8y-2y-(x+y)]-x+(3y-10z)]=? kuai 二元函数f(x,y)=x+y/x-y,求f(y/x,x/y) 9y=3x-(x-1),4(x+y)-(2x+4)=8y 设X,Y是正实数,而且X+4Y=4,求XY的最大值~ [x(x-y)-y(x-y)+(x+y)(x-y)]÷2x其中x=2012 y=2013 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）