7+(x-3y)/4=2x-(y+5)/3,[10(x-y)-4(1-x)]/3=y帮解一下啊!

化简[(3x+4y)^2-(2x+y)(2x-y)+(-x+y)(5x-y)]除以-2y,其中x=-1,y=1 已知x=1/3,y=-1/2,求代数式x-(x+y)+(x+2y)-(x+3y)+(x+4y)-(x+5y)+...-( {3(x+y)-4(x-y)=4 {x+y/2 + x-y/6=1 3(x+y)-4(x-y)=11,2(x-y)+5(x+y)=27 (4x-2y-z)-{5x[8y-2y-(x+y)]-x+(3y-10z)]=? kuai 解方程组：（0.2x+0.1y）/2- （4x-y）/10=（x-y）/5+ (3x+0.5y)/30 (3x+2y-1 请帮我做几道方程1、x+2y=0 3x+4y-6=02、3x+2y=-2 3x-y=43、6x+7y=-19 5y-6x 化简求值3x-2y-5xy-（2x-3y+2xy）,其中x+y=4,xy=-7,x和y并没有解出来啊,请解一下啊,帮 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 数学题……555{(3x+y)(3x-y)-(x-5y)(5x-y)-(x-2y)²÷(-4x),x=-2.y 若2x-3y+4=0则x（x*x-1)+x(5-x*x)-6y+7 已知x-y/x+y=3,求代数式5(x-y)/x+y-x+y/2(x-y)