maths 問題

2x+3y=2---(1)
3x-4y=20---(2)
(1)*3-(2)*2
3(2x+3y)-2(3x-4y)=(2)(3)-(20)(2)
6x+9y-6x+8y=6-40
17y= -34
y= -2---(3)
Sub (3) into (2)
3x-(4)(-2)=20
3x+8=20
3x=12
x=4

∴x=4, y= -2

2x+3y=2--------(1)
3x-4y=20
From(1),we can know that y=negative number.
Let:
x=4
y=-2
2(4)+3(-2)=2
3(4)-4(-2)=20
So x=4
y=-2

2x+3y=2 ----1
3x-4y=20 ----2

2 減 1
x-7y=18
x=18+7y

2x+3y=2
2(18+7y)+3y=2
36+14y+3y=2
17y= -34
y= -2

x=18+7y
x=18+7(-2)
x=4

{2x+3y=2---
3x-4y=20---
由,
2x+3y=2
2x=2-3y
x=2-3y/2
代x=2-3y/2入
3(2-3y/2)-4y=20
3(2-3y)-8y=40
6-9y-8y=40
6-17y=40
-17y=34
y=-2
代y=-2入
2x+3(-2)=2
2x+(-6)=2
2x-6=2
2x=8
x=4

x=5
y=1.2