4x+3y=1 x=y=7/1 怎么算的

4x+3y=1 x=y=7/1 怎么算的 已知x-y=1,求[(x+2y)²+(2x+y)(x-4y)-3(x+y)(x-y)]÷y的值 已知x-y=1,求[(x+2y)^2+(2x+y)(x-4y)-3(x+y)(x-y)]除以y的值大神们帮帮忙 7x-3y=-1 4x-5y=-17方程组怎么算? 7x-3y=-1怎么变形?y=? 若2/x-1/y=3,求[y/x-y/x-y(x-y/x-x+y)]/x-2y/x的值 (-x+6):(x-y);(4x+y)=3;14:1,求x+y的值. 先化简,再求值[2x的平方-(x+y)(y-x)][3(-x-y)(y-x)+4y的平方]其中x=三分之一y=1 若x=-1/4,能否确定代数式(2x-y)(2x+y)+(2x-y)(y-4x)+2y(y-3x)的值? (2x+y-1)(2x-y-1)=?和（3x+y-5a）的平方怎么算 已知(3x+1)(3x-3)-3x+2)^2=-7,(y+7)(y-7)-y(y-7)=0,求8y^2-5y(-y+3x)+4y(-4y-5/2x)的值 对于(y一撇）y`=y/x(y-1)求导,我求的结果是y``=-y^2-y`x+y/x^2(y-1)^2 怎么不对啊,我的求导过程是：y`x(y-1) - [x(y-1)]` y y`xy-y`x-(y-1+xy`)y -y^2-y`x+yy``=-------------------------=----------------------=-----------------x^2 (y-1 {3(x+y)+3(y+x)=1,3(x+y)+4(y-x)=-1 {3(x+y)-4(x-y)=4 {x+y/2 + x-y/6=1 x^2-4Y^2+X+3Y-1=0 2X-Y-1=0 怎么算 y=(x^2-4x-5)/(x^2-3x-4)的值域是答案是y≠1且y≠6/5怎么算的? 已知x×x×y×y+x×x+y×y+1=4xy,求x,y的值快 x+x+x+y+y=6.4 y+y+y+x+x=7.1 怎么算? 4x方y/(x-2y)(x+2y)怎么算[x方/x-2y]-4x方y/(x-2y)(x+2y)=?