x+y/y=13/8,1/x+1/y=13/40
已知x=3分之1,y=二分之一,求代数式x-(x+y)+(x+2y)-(x+3y)+...-(x+13y)的值
已知:3x=8y.求(1)x+y/y (2)2x+3y/x-2y
解方程组: {3x+2y=13 3x-2y=5 {x-y/3=x+y/2+1 2x-5y=9
y'=(x-y+1)/(x+y-3)通解
{2x-5y=21,{2x+y=6 {x-3y=1 {y=-2x+3 y=-x; y=1/2x+1 5x-9y=-13
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
9y=3x-(x-1),4(x+y)-(2x+4)=8y
y=[x-1],
1.已知1/x+1/y=-1/x+y,则y/x+x/y=?
{3(x+y)+3(y+x)=1,3(x+y)+4(y-x)=-1
{4/(x+y)+6/(x-y)=3 {9/(x-y)-1/(x+y)=1
(3x-y)^2+(3x+y)(3x-y),x=1,y=-2