5x+5*4/7x=y*2 5*x+5y=0

已知x*x+4x+y*y-2y+5=0,则x*x+y*y=? 若2x-3y+4=0则x（x*x-1)+x(5-x*x)-6y+7 若(x*x+y*y)(x*x+y*y)-4x*x*y*y=0,求代数式(x*x+5xy+y*y)/(x*x+2xy+y* 解方程组(x+y)(x-2y)=-5 (x-y)(x+2y)=7 3(x+y)-4(x-y)=11,2(x-y)+5(x+y)=27 已知x^2+4y^2-4x+4y+5=0,求(y^4-x^4)/(y-2x)(x+y)*2x-y .先化简再求值：（2x+y）（2x+y)-(2x-y)平方其中X,Y满足X平方+Y平方-2X+4Y+5=0 已知X.x+y.y-4x+2y+5=0,求4X.X-12X Y+9Y.y的值 已知x-y/x+y=3,求代数式5(x-y)/x+y-x+y/2(x-y) y-3x=2,y-5x=4,y-7x=6,y-9x=8,y-11x=0方程组, x-y+5x-4x= ? 数学题……555{(3x+y)(3x-y)-(x-5y)(5x-y)-(x-2y)²÷(-4x),x=-2.y