y=(20+x)(80-2x) =-2x²+40x+1600怎么算

x-y/x-x+y/y-(x+y)(x-y)/y² y/x=2 x+y/2+x-y/3=6,4(x+y)-3(x-y)=-20 {(x+y)/2+(x-y)/3=6 4(x+y)-3(x-y)=-20 4(x+y)-3(x-y)=-20,2/x+y+3/x-y=6 y=x^2-2x（x y=x^2+2x(x 3^x+2x=y,x 填空：x-y/x+y=( )/x^2-y^2 （x-y)2•(y-x)³(x-y)=? x²-(x-2y)(x+2y)+(x²-y)(y+x²)=? (x-y) (x-2y)+(x+2y) (x-3y)-2(x-3y) (x-4y)= (x+y)(x-y)+(x-y)平方-(x-y)(3x-y) 其中x=-2 y=3分之一 已知x-y/x+y=3,求代数式5(x-y)/x+y-x+y/2(x-y) (x-4y)(2x+y)= (x+y)(2x-3y)=? x+y>=2,x-y x+y>=2,x-y y'-2y=(e^x)-x