①40x=440+y!②30x=310+y

x+y=450;40%x+30=60%y (x+y)(x+2y)(x+3y)(x+4y)=-40 已知x+y,且x²-2x=7,y²-2y=7求①x+y②2x+xy+y² 已知x^2+y^2=10,x+y=4,求①2xy ②(x-y)^2 ③x-y ④x^2-y^2 二元函数f(x,y)=x+y/x-y,求f(y/x,x/y) [x(x-y)-y(x-y)+(x+y)(x-y)]÷2x其中x=2012 y=2013 ① X+Y=3 Y=2X-3 ② x+2y=9 y-3x=1 ③3/x+1=y 2（x+1)=6 ④ y-x=3 7x- 下列函数：①y=-3x②y=2x-1；③y=-1/x（x 下列函数：①y=-3x；②y=2x-1；③y=-1/x（x ) y=cos(x-y) x+y=5; x^y+y^x=17 因式分解下列式子：x(x-y)+y(y-x)=?