化简[21x^5y^7-28x^7y^4＋7y(2x³y²)²]÷(-7x^5y^4）

化简{21x^5y^7-28x^7y^4+7y(2x^3y^2)^2}/(-7x^5y^4) 化简[21x^5y^7-28x^7y^4＋7y(2x³y²)²]÷(-7x^5y^4） 化简2（2X-7Y)(7Y+2X)+X^2-(-4X+5Y)(-5Y-4X) 化简:3(x-y)²-7(x-y)+ 2(x-y)²+5(x-y) {6(x-y)-7(x+y)=21 {2(x-y)-5(x+y)=-1 (3x-4y)(5x-4y)-(7x-8y)(6y-5x) 把(x-y)看作一个整体,化简:(1)5(x-y)+2(x-y)-4(x-y);(2)3(x-y²-4(x-y)+7（x-y)-6(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) 填空：（一）20x^2+（）+14y^2=(4x-7y)(5x-2y) （二）x^2-3xy-（）=(x-7y)(x+4y)（一）20x^2+（）+14y^2=(4x-7y)(5x-2y)（二）x^2-3xy-（）=(x-7y)(x+4y)（三）x^2+（）-28y^2=(x+7y)(x-4y)（四）x^2+（）-21y^2=(x-7y)(x+3y) 化简3(x-y)-7(x--y)+2(y-x) 化简 3(X-Y)²-4(X-Y)+7(X-Y)-6(X-Y)²3(X-Y)²-4(X-Y)+7(X-Y)-6(X-Y)²(X-Y)视为整体 (x+5y)(x-7y-1) 7x:4y,x:y=( ):( 21/(x+y)+4/(x-y)=12/(x+y)+7/(x-y)结果为(x+y)/(x-y)=3求过程! 把(x-y)看作一个整体,化解:5(x-y)+2(x-y)-4(x-y)= 3(x-y)把(x-y)看作一个整体,化解:5(x-y)+2(x-y)-4(x-y)=3(x-y)²-4(x-y)+7(x-y)-6(x-y)²= 化简 2x-[3y-5x-(-2x-7y)]等于 （ ） A：-7x+10y B：5x+4y C:-x-4y D:9x-10y 7.5x+7y=52 5x+2y=22 8.5x+5y=65 7x+7y=203 9.7.5x+7y=52 5x+2y=22 8.5x+5y=65 7x+7y=203 9.8x+4y=56 x+4y=21 17.3x+8y=51 x+6y=27 18.9x+3y=99 4x+7y=95 19.9x+2y=38 3x+6y=18 20.5x+5y=45 7x+9y=69 21.8x+2y=28 7x+8y