1、1/4x-1/5y=3

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)+...-( 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 {3(x+y)+3(y+x)=1,3(x+y)+4(y-x)=-1 3x-2y=1 4x-5y ｛4/(x+y)+6/(x-y)=3 ｛9/(x-y)-1/(x+y)=1 （x+2)(x+3) (x-4)(x+1) (y+4)(y-2) (y-5)(y-3) {3(x+y)-4(x-y)=4 {x+y/2 + x-y/6=1 化简求值{(x=2y)(5x-2y)-(3x+2y)(3x-2y)]/4x,其中x=2,y=-1 3x+2y/4=2x+y/5=x-y+1/6 微分方程(1)(y'')^2+5y'-y+x=0;(2)y''+5y'+4y^2-8x=0;(3)(3x+2y)dx+( 若2x-3y+4=0则x（x*x-1)+x(5-x*x)-6y+7