x+y=9, x-y=3 则2x^2- 2y^2的值是多少?要过程.

x-y/x-x+y/y-(x+y)(x-y)/y² y/x=2 3(x+y)-2(x-y)=11 4(x+y)+3(x-y)=9 4(x-y)-3(x-y)=9 5(x-y)+2(x-y)=11 若(x-y)/(x+y)=3 则(x+2y)/(6x-7y)等于 若2x=3y,则(x*x+y*y)/x*x=? (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+y)(2x-3y)=? 若2x+3y=2004,则代数式2(3x-2y)-(x-y)+(-x+9y)=... 若2x+y=2012,则代数式2(3x-2y)-(x-y)+(-x+9y)= x+y=9 x-y=3则2x²-2y²= 已知x-2y=3,则(2x+y-6)/(3x-y-9)=? 3^x+2x=y,x 9y=3x-(x-1),4(x+y)-(2x+4)=8y 5x=3y,(2x+y)的平方=5x(x+y)+9 已知2x=3y,则y分之x=< >,y分之x+y=< >. 若2/x-1/y=3,求[y/x-y/x-y(x-y/x-x+y)]/x-2y/x的值