maths?入消元法

{3x-4y-1=0 ... [1]
{2x+3y-4=0 ... [2]

2*[1] - 3*[2]
2(3x-4y-1) - 3(2x+3y-4) = 0
6x-8y-2 - 6x-9y+12 = 0
17y = 10
y = 10/17

sub into [1]
3x-4*10/17-1 = 0
3x = 57/17
x = 19/17


{5x+3y+6=0 ... [1]
{3x-2y-23=0 ... [2]

2*[1] + 3*[2]
2(5x+3y+6) + 3(3x-2y-23) = 0
10x+6y+12 + 9x-6y-69 = 0
19x = 57
x = 3

sub into [2]
3*3-2y-23 = 0
2y = -14
y = -7


{2(x+y)-3x=4 ... [1]
{3(x-y)+5y=12 ... [2]

[1]　2(x+y)-3x=4
　　2x+2y-3x=4
　　x = 2y-4 ... [3]

sub into [2]
3(2y-4-y) + 5y = 12
3y - 12 + 5y = 12
8y = 24
y =3

sub into [3]
x = 2*3-4
x =2


{3x-2y=2 ... [1]
{x-y/2=-4 ... [2]

[1] - 4*[2]
(3x-2y) - 4(x - y/2) = 2 - 4*(-4)
3x-2y - 4x+2y = 2+16
-x = 18
x = -18

sub into [1]
3(-18) - 2y = 2
2y = -56
y = -28

{3x-4y-1=0 -----(1)
{2x+3y-4=0 -----(2)

(1)乘2

6x-8y-2 =0 ----(3)

(2)乘3

6x+9y-12 =0 ----(4)

(4) - (3)

6x-6x+9y-8y-12-2=0
y-14=0
y=14

y 代入 (1)

3x-4(14)-1=0
3x=55
x=55/3