x+x+x+y=42 x+y+y+y=30 求x=( )y=( )

二元函数f(x,y)=x+y/x-y,求f(y/x,x/y) 求y'=y/(y-x) 已知X-Y/X+Y=3,求代数式2(x-y)/X+Y-3X+Y/X+Y 已知x-y/x+y=3,求代数式5(x-y)/x+y-x+y/2(x-y) (x*x+y*y)(x*x+y*y)-(x*x+y*y)=12 求x*x+y*y等于多少 x+x+x+y=52 y+y+y+x=36求x 求微分方程y'=x/y+y/x的通解 y=2x*arctan(y/x),求y‘’ 已知：4x = 5y,求(x+y) ：y [x(x-y)-y(x-y)+(x+y)(x-y)]÷2x其中x=2012 y=2013 |x-y |=x-y |x |=1999 |y |2000,求x+y的值 已知/x/+x+y=10,/y/+x-y=12.求x+y的值