化简2(4x-6y)-3(2x+3y-1) ,化简1÷2（2x－4y）＋2y ,已知道等腰三角形的底是（4a－2b）cm,腰是（a＋b）cm,则此等腰三角形的周长是?

{3(x+y)-4(x-y)=4 {x+y/2 + x-y/6=1 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) 化简[(3x+4y)^2-(2x+y)(2x-y)+(-x+y)(5x-y)]除以-2y,其中x=-1,y=1 1/(x-y)+1/(x+y)+2x/(x^2+y^2)+4x^3/(x^4+y^4)化简 x²/xy-x/y 3x/4x+y - x-2y/4x+y (1-y/y+x)÷x/y²-x² 化简：{2/3x-2/(x+y)[(x+y)/3x-x-y]}/(x+y)/x 化简3x-2/(x+y)[(x+y)/3x-x-y]÷(x-y)/x 化简(x+y)-(2x+y/2)-(3x+y/6)-(4x+y/12)-(5x+y/20)-……-(10x+y/90) 解二元一次方程组：3(x+y)-4(x-y)=4,x+y/2+x-y/6+1x+y/2+x-y/6+1=1 化简:(x-3y)(x+y)-(x-2y)(x+2y)-(x-y)平方 x+y/2+x-y/3=6,4(x+y)-3(x-y)=-20 {(x+y)/2+(x-y)/3=6 4(x+y)-3(x-y)=-20 4(x+y)-3(x-y)=-20,2/x+y+3/x-y=6 4x-3y/x-2y÷6y-8x/y-2x （x+y）/2- x-y/2=6 3(x+y)=4(x-y) x+y/3+x-y/2=6 4(x+y)-2(x-y)=40 81/8*(-x-y)^6*(x-y)^3*4/9(x+y)^4*(y-x)^2 （y-x）^4（x-y）^3+2（x-y）^6（y-x）