求z=2x+y的概率密度 ①x+y+z=6 3x-y+2z=12 x-y-3z=-4 ②x+y-z=2 4x-2y+3y+8=0 x+3y-2z-6=0③x/3=y/2 y/4=z/5 x+y+z=6

①x+y+z=6 3x-y+2z=12 x-y-3z=-4 ②x+y-z=2 4x-2y+3y+8=0 x+3y-2z-6=0③x/3=y/2 y/4=z/5 x+y+z=60  

①x+y+z=6 3x-y+2z=12 x-y-3z=-4 ②x+y-z=2 4x-2y+3y+8=0 x+3y-2z-6=0③x/3=y/2 y/4=z/5 x+y+z=60

(1)x+y+z=6 ①3x-y+2z=12② x-y-3z=-4 ③
①+②4x+3z=18 ④ ②-③2x+5z=16⑤
⑤×2 4x+10z=32⑥ ⑥-④7z=14 解得z=2 代入⑤2x+5×2＝16解得x=3
将x=3 z=2 代入①3+y+2=6解得y=1
x=3 y=1 z=2
(2)x+y-z=2① 4x-2y+3z+8=0 ②x+3y-2z-6=0③
①×4 4x+4y-4z=8④ ④-②6y-7z=16⑤
③-① 2y-z=4 将 z=2y-4代入⑤6y-7(2y-4)=16解得y=1.5 z=2×1.5-4=﹣1
将y=1.5 z=-1代入①x+1.5-（-1）=2解得x=-0.5
x=-0.5 y=1.5 z=-1
(3)x/3=y/2① y/4=z/5② x+y+z=60③
由①得x=3/2y 由②得z=5/4y 代入③3/2y+y+5/4y=60解得y=16
x=3/2×16=24 z=5/4×16=20
x=24 y=16 z=20

若x/2=y/3=z/4,则3x-2y+5z/x+y+z=

设x/2=y/3=z/4=a则,x=2a,y=3a,z=4a则3x-2y+5z/x+y+z=6a-6a+20a/2a+3a+4a=20/9

若x/2=y/3=z/4且x+y+z=-27,这x+2y+3z=（）

x/2=y/3=z/4
y=3x/2
z=2x
所以x+y+z=x+3x/2+2x=-27
9x/2=-27
x=-18
所以原式=x+3x+6x
=10x
=-180

X/2=Y/3=Z/5,X+Y+Z=8,X=?

令X/2=Y/3=Z/5=k,
x=2k, y=3k, z=5k,代入X+Y+Z=8。
2k+3k+5k=8, k=0.8
x=2k=1.6
y=3k=2.4
z=5k=4

已知x/2=y/3=z/4且x+y+z=12求2x+3y+4z

x/2=y/3=z/4
x+y+z=12
x=8/3
y=4
z=16/3
2x+3y+4z=38+2/3

已知x/3=y/4=z/2,求x+2y-z/x+y+z=？

x=y乘三分之四=z乘二分之三 由此得出：x=四分之三y=二分之三z y=三分之四 z=三分之二 x=1,再把数字带到x+2y-z/x+y+z中去，如果还不懂。就加我qq，2369131626

若x=y/2=z/3,且x+y+z=12，2x+3y+4z=？

解：
若x=y/2=z/3,则
y=2x
z=3x
且有x+y+z=12,则
x+2x+3x=12
x=2
y=4
z=6

2x+3y+4z=4+12+24=40

x/2=y/3=z/4=4，且3x-2y+5z=-20.x+3y-z=

设x/2=y/3=z/4=m
则x=2m,y=3m,z=4m
3x-2y+5z=20
6m-6m+20m=20
20m=20，m=1
x=2,y=3,z=4
x+3y-z=2+3×3-4=7

x/4=y/5=z/6 2x+3y-4z+3=0

令x/4=y/5=z/6=k
则，x=4k,y=5k,z=6k
∴2x+3y-4z+3=0即
8k+15k-24k+3=0
解得，k=3
∴x=12,y=15,z=18

已知x/2=y/3=z/4,且x+y+z不等于0,求2x+3y-4z/x+y+z的值

x/2=y/3=z/4=k
x=2k,y=3k,z=4k
2x+3y-4z/x+y+z
=(4k+9k-16k)/(2k+3k+4k)
=-1/3