(x+5y)(x-7y-1)

x+y=3 x+2y=9 3/x+1=y y-x=3 y=2x-3 y-3x=1 2(x+1)-y=6 7x-5y=-9 1) (2x+5y)(2x-5y)(-4x^2-25y^2) 2) [（x+y)(x-y)-(x-y)^2+2y(x-y 7x-3y/5=5x-y/3-x+y/2 x-1/5=y+1/3 { x-y/7-x+y/10=1/2 {2(x-y)+5(x+y)=3 已知：x-y=1,x+y=-7,求代数式3（x+y)+20(x-y)-5的值 先化简再求值(x-y)(x+y)-(x-2y) 的完全平方+x(3x-5y)-(x-y)(x-2y),其中x=1/2 y 若7x+10y分之5x+y=1/2,则x/y= 1、x(x-y)(x+y)-x(x+y)^2 (3x-4y)(5x-4y)-(7x-8y)(6y-5x) 解方程组(x+y)(x-2y)=-5 (x-y)(x+2y)=7 （x+2)(x+3) (x-4)(x+1) (y+4)(y-2) (y-5)(y-3) 计算(x^8-x^7y+x^5y^3-x^4y^4+x^3y^5-x^y^7+y^8)(x^2+xy+y^2)