7x-3y=-12 4x+2y=-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 已知x-y/x+y=3,求代数式5(x-y)/x+y-x+y/2(x-y) 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)+...-( 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 若2x-3y+4=0则x（x*x-1)+x(5-x*x)-6y+7 若x-2y=5,则式子12-x+2y=.以知3x-4y=2x+y则x∶y= 3x+2=y 5X+4=Y 7X+6=Y 9X+8=y 11x=y要如何计算 3x+2=y 5x+4=y 7x+6=y 9x+8=y 11x=y y-3x=2,y-5x=4,y-7x=6,y-9x=8,y-11x=0方程组,