{x-y=4 {3x+4y=19

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{x-y=4 {3x+4y=19

x-y=4.1
3x+4y=19.2
由1式得
x=y+4.3
将3式代入2式得
3(y+4)+4y=19
3y+12+4y=19
7y+12=19
7y=7
y=1
将y=1代入3式得
x=1+4=5
所以x=5,y=1

{3(x+y)-4(x-y)=4 {x+y/2 + x-y/6=1 {3(x+y)+3(y+x)=1,3(x+y)+4(y-x)=-1 （5x+3y)(3y-5x)-(4x-y)(4y+x)= x+y/2+x-y/3=6,4(x+y)-3(x-y)=-20 {(x+y)/2+(x-y)/3=6 4(x+y)-3(x-y)=-20 4(x+y)-3(x-y)=-20,2/x+y+3/x-y=6 3(x+y)-4(x-y)=11,2(x-y)+5(x+y)=27 ｛4/(x+y)+6/(x-y)=3 ｛9/(x-y)-1/(x+y)=1 (x+y)(x+2y)(x+3y)(x+4y)=-40 {x-y=4 {3x+4y=19 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)+...-(