2x+5y=20,求x,y.

已知x-y/x+y=3,求代数式5(x-y)/x+y-x+y/2(x-y) 已知x=1/3,y=-1/2,求代数式x-(x+y)+(x+2y)-(x+3y)+(x+4y)-(x+5y)+...-( 已知x²+y²+5=2x+4y,求【2x²-(x-y)(x-y)】【(x+y-1)(x-y 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* 已知X-Y/X+Y=3,求代数式2(x-y)/X+Y-3X+Y/X+Y 求y''-2y'+5y=(e^x)sin2x 求dy/dx=(x-y+5)/(x+y-2) 若x-y/x+y=5,求x-y/2x+2y+5x+5y/3x-3y的值 已知x^2+4y^2-4x+4y+5=0,求(y^4-x^4)/(y-2x)(x+y)*2x-y 如果x,y表示有理数,且x、y满足条件,|x|=5,|y|=2.|x-y|=y-x,求：x+2y的值. 已知X.x+y.y-4x+2y+5=0,求4X.X-12X Y+9Y.y的值 已知x²+y²+5=2x+4y,求代数式（2x²-（x+y)(x-y))x((x+y-1)