6x^2-7xy-3y^2+13x+8y-5用双十字相乘法

1、(-7x^y)(2x^y-3xy^3+xy) 2、((x-y)^6)/((y-x)^3)/(x-y) 3(x-y)²-7(x-y)+8(x-y)²+6(x-y)求详细过程（2） 5xy-4x²y-8xy²+3xy-xy²+4x²y x+y=8,xy=-2,求(5xy+4x+7y)+(6x-3xy)-(4xy-3y)的值 诺x+y=6,xy=4 求(5x-4y-3xy)-(8x-y+2xy) 化简：x-y/x+3y÷x^-y^2/x^2+6xy+9y^2-(xy/x+y) 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) 因式分解 x-xy+3y-3x 2x+xy-y-4x+5y-6 因式分解:8(x-2y)-x(7x+y)+xy. 化简求值x-4y/2x-7xy+3y×x-2xy-3y/2x+3xy-2y÷3x-6y/4x-4xy+y,其中：x=1999,y=-1 (x-2xy)*(-xy+2y*y)-(3x*x-2xy)(x-9xy+6y*y)答案应为-2x-x*x-3x， x^2-xy-6y^2+3xy+y+2 因式分解：4x^2+8xy+3y^2-6x-7y+24x^2+8xy+3y^2-6x-7y+2 3y/x*x-y*y+x/x*x-2xy+y*y+6y*y/x*x*x-x*x*y-xy*y+y*y*y等于多少? 化简：3x^2-[5xy-(x^y-3xy)+4x^2y-8xy] 已知1/x-1/y=2,求3x+7xy-3y/2x-3xy-2y答案是1/x-1/y=2(y-x)/xy=2 得：x-y=-2xy(3x+7xy-3y)/(2x-3xy-2y)=[3(x-y)+7xy]/[2(x-y)-3xy]=(-6xy+7xy)/(-4xy-3xy)=xy/(-7xy)=-1/7 谁能帮我解释一下=[3(x-y)+7xy]/[2(x-y)-3xy]=(-6xy+7xy)/(-4xy-3xy) 是怎 (8X^3Y-6X^2Y^2-2XY^3)/(3XY) (8X^3Y-6X^2Y^2-2XY^3)/(3XY) x^2+xy-6y^2+x+13y-6