2x+5y=25 5x+3y=12

已知x-y/x+y=3,求代数式5(x-y)/x+y-x+y/2(x-y) 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 6(x-y)-2(x+y)=14 3(x-y)+(x+y)=5 3(x+y)-4(x-y)=11,2(x-y)+5(x+y)=27 解方程组：x+y/2+x-y/3=6 4(x+y)-5(x-y)=12 化简[(3x+4y)^2-(2x+y)(2x-y)+(-x+y)(5x-y)]除以-2y,其中x=-1,y=1 5(x-y)^3*[-6/25(y-x)^3][-2/3(y-x^4]= 已知x=1/3,y=-1/2,求代数式x-(x+y)+(x+2y)-(x+3y)+(x+4y)-(x+5y)+...-( 数学题……555{(3x+y)(3x-y)-(x-5y)(5x-y)-(x-2y)²÷(-4x),x=-2.y (4x-2y-z)-{5x[8y-2y-(x+y)]-x+(3y-10z)]=? kuai 5(x+y-2)=3-y 若x-2y=5,则式子12-x+2y=.以知3x-4y=2x+y则x∶y=