7x^2+3y+xy+21x2ac-6ad+bc-3bd

7x^2+3y+xy+21x2ac-6ad+bc-3bd 已知A=8x^2y-6xy^2-3xy,B=7xy^2-2xy+5x^2y求A-B 1、(-7x^y)(2x^y-3xy^3+xy) 2、((x-y)^6)/((y-x)^3)/(x-y) 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 因式分解30题(要过程)am+an+bm+bn x^2+5y-xy-5x x2+xy+2xz+x (a+b)x-(b+a)y -12x(x-y)-(y-x)x^2 2x^2+4x+2 x(x+z)-y(y+z) 2(x^2-3ab)+x(4a-3b) 4x^2+12xy+9y^2-25 x^4-16 16x^4-1 x^2+9x+8 x^2-10xy+24y^2 2x^2+15xy-8y^2 3x^2-6xy+3y^2 24x^2+22x-21 -x^2+4xy- (1)x^n+2 -6x^2+n +8x^2(2)x^2 -21xy +98y^2 +x -7y(3)x^2 +6xy +9y^2 -4a^2 +4ab -b^2 计算以及化简：3a²-[7a²-2a-3（a²-a）+1]还有呢：（8-x²y+7xy²-6xy)-[8xy-(x²y+y²x)] x^2-xy-6y^2+3xy+y+2 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 (14x^3*y-7x^2*y^2+21xy^3)/(-7xy) 计算 (21xy^3-7x^2y^2+28x^3y)÷(-7xy) 已知A=8x^2y-6xy^2-3xy,B=7xy^2-2xy+5x^2y,且C=3（A+B),求C-2A的值 若A=8x^2·y-6xy^2-3xy.B=7xy^2-2xy+5x^2y.且C=3(A+B).求C-2A的值. 已知A=8x^2y-6xy^2-3xy,B=7xy^2-2xy+5x^2y,A+B-3C=0,求C-A 已知A=8X^2Y-6XY^2-3XY,B=7XY^2-2XY+5X^2Y,若A+B-3C=0,求C-A. 已知A=2x的二次方y-6xy的二次方-3xy,B=7xy的二次方-2xy+5x的二次方y若A+B=3C,求C-A 若A=8x²y-6xy²－3xy,B=7xy²－2xy+5x²y且C=3（A+B）.求C－2A x+y=8,xy=-2,求(5xy+4x+7y)+(6x-3xy)-(4xy-3y)的值