The first group of equations: 2x + y = 4,2y + Z = - 3,2z + x = 5, the second group of equations: X / 2 = Y / 3 = Z / 4,5x + 2y-3z = 8 Don't copy it

The first group of equations: 2x + y = 4,2y + Z = - 3,2z + x = 5, the second group of equations: X / 2 = Y / 3 = Z / 4,5x + 2y-3z = 8 Don't copy it

The first set of equations: 2x + y = 4 (1)
,2y+z=-3 （2）
,2z+x=5 （3）
From (1) * 2 - (2)
4x-z=11 (4)
From (4) * 2 + (3)
8x-2z+2z+x=11*2+5
9x=27
x=3
y=-2
z=1
The second set of equations: X / 2 = Y / 3 = Z / 4
x=z/2
y=3z/4
5x+2y-3z=8
5*z/2 +2*3z/4-3z=8
5z +3z-6z=16
z=8
x=4
y=6
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Equations X / 3 = Y / 4 = Z / 5, x-2y = 3Z = 30

Let X / 3 = Y / 4 = Z / 5 = K
therefore
x=3k
y=4k
z=5k
Bring in the following formula:
3k-8k+15k=30
k=3
So x = 9
y=12
z=15

Solve the equations {x + 2Y + Z = 4 2x + y + 2Z = 5 x + y + 3Z = 5
Make it clear

x+2y+z=4 ①
2x+y+2z=5 ②
x+y+3z=5 ③
2①-③＝3y＝3
y＝1 ④
②-③＝x-z＝0
x＝z ⑤
Substitute (4) and (5) into (1)
x+2+x=4
x=1=z
So x = 1, y = 1, z = 1

If 2x + 3Y = 0, then 2x + 7Y / 4x-2y=______ .
To complete the process
(y is not equal to 0)

2x+3y=0
Then 2x = - 3Y
2x+7y/4x-2y
=(-3y+7y)/(-6y-2y)
=(4y)/(-8y)
=-1/2