二元一次方程10點(緊急)thx

4y+3x+2z=45 --- (1)
3y+2x+4z=33 ---(2)
2y+4x+3z=30 ---(3)

(1) + (2) +(3)
9y + 9x + 9z = 108
y+x+z = 12 --(4)
(4) x 4
4y + 4x + 4z = 48 --(5)
(5) - (1)
x + 2z = 3 ---(6)
(4) x 3
3x + 3y + 3z = 36 (5)'
(5)' - (2)
x - z = 3 ---(7)
(6) - (7)
3z = 0
z = 0
sub. into (7)
x = 3
sub. into(4)
y = 9

x = 3, y = 9, z = 0

4y + 3x + 2z = 45 ...........(1)
3y + 2x + 4z = 33 ...........(2)
2y + 4x + 3z = 30 ...........(3)

(1)*2 - (2)
(4y + 3x + 2z)*2 - (3y + 2x + 4z) = 45*2 - 33
8y + 6x + 4z - 3y - 2x - 4z = 57
5y + 4x = 57 ................(4)

(1)*3 -(3)*2
(4y + 3x + 2z)*3 - (2y + 4x + 3z)*2 = 45*3 - 30*2
12y + 9x + 6z - 4y - 8x - 6z = 75
8y + x = 75 ...............(5)

(5)*4 - (4)
(8y + x)*4 - (5y + 4x)= 75*4 - 57
32y + 4x - 5y - 4x = 243
27y = 243
y = 9

Put y = 9 into (5)
8*9 + x = 75
72 + x = 75
x = 3

Put x = 3, y = 9 into (1)
4*9 + 3*3 + 2z = 45
36 + 9 + 2z = 45
z = 0

Therefore, x = 3, y = 9, z = 0

4y+3x+2z=45-------------1
3y+2x+4z=33-------------2
2y+4x+3z=30-------------3

(3)*2-1
4y+8x+6z-4y-3x-2z=30*2-45
4z=15-5x------------4
z=(15-5x)/4-----------5

put 4 into 2
3y+2x+15-5x=33
y=6+x-----------------6

put 5,6 into 1
4(6+x)+3x+(15-5x)/2=45
x=3

put x = 3 into 6
y=9

put x=3 into 5
z=0