x+y-z=5 2x+3y+z=10 x-2y-z=20 速解,

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x+y-z=52x+3y+z=10x-2y-z=20速解,x+y-z=52x+3y+z=10x-2y-z=20速解,x+y-z=52x+3y+z=10x-2y-z=20速解,x+y-z=5(1)2x+

x+y-z=5 2x+3y+z=10 x-2y-z=20 速解,
x+y-z=5 2x+3y+z=10 x-2y-z=20 速解,

x+y-z=5 2x+3y+z=10 x-2y-z=20 速解,
x+y-z=5 (1)
2x+3y+z=10 (2)
x-2y-z=20 (3)
(1)+(2)
3x+4y=15 (4)
(2)+(3)
3x+y=30 (5)
（5）-（4）
-3y=15
y=-5
代入(5)
3x-20=15
x=35/3
代入(1)
35/3-5-z=5
z=5/3
所以
x=35/3,y=-5,z=5/3
要（4）-（5）而不是（5）-（4）,或是（5）+（4）主要是为了消元只有消元才能解除来你采用（5）+（4）怎么消元没用的!

x+y-z=5~~~~~~~~~~~A
2x+3y+z=10~~~~~~~~B
x-2y-z=20~~~~~~~~~~C
A-C得
y＝-5
带入AB
A+B得
x＝35/3
z＝5/3

列方程组啊！三元一次方程组，解就行。

x=9
y=-3
z=-5 计算超级麻烦，LZ想要可以追问，我回答你！

(4x-2y-z)-{5x-[8y-2z-(x-2y)]-x-(3y-10z)}=? x/2=y/3=z/5 x+3y-z/x-3y+z x+2y+3z=23 y-z=5 x+2z=10 (4x-2y-z)-{5x-[8y-2z-(x+y)]-2(3y-10z)}=?好难啊已知(x+y)(x+z)=x,(y+z)(y+x)=2y,(z+x)(z+y)=3z,求x,y,z 试证明(x+y-2z)+(y+z-2x)+(z+x-2y)=3(x+y-2z)(y+z-2x)(z+x-2y) 已知x-y/x+y=y+z/2(y-z)=z+x/3(z-x),求证8x+9y+5z=0THX.. (4x-2y-z)-{5x[8y-2y-(x+y)]-x+(3y-10z)]=? kuaihuajian X=3z X+y+z=12 X+2y-2z=10 2x+z=10 x+y-z=4 3x-y-z=0 X/10=Y/8=Z/9,则X+Y+Z/2Y-3Z 3x+2y+z=14 ,x+y+z=10,z+2x+3y=1 5 x+y+2z=5 2x-y-z=4 3x+y-3z=10 {2x+3y-4z=-5 x+y+z=6 x-y+3z=10 2x+y-z=3 5x+3y-z=10 求x+y+z= -2X+3Y+Z=-4-X-5Y-2Z=-13X+Y-Z=10 x+y-z=5,2x+3y+z=10,x-2y-z=20求方程组 x+y-z=5 2x+3y+z=10 x-2y-z=20 速解,