Maths 聯立方程

1.
x+y=16______________________(1)
x-y=8_______________________(2)

(1)+(2):
2x=24
x=12

把x=12代入(2) ,可得
12-y=8
y=4

2.
x+3y=13______________________(1)
2x-3y=8______________________(2)

(1)+(2)
3x=21
x=7

把x=7代入(1) ,可得
7+3y=13
3y=6
y=2


3.
x=2y+5_________________(1)
2x-3y=11________________(2)

把(1)代入(2) ,可得
2(2y+5)-3y=11
4y+10-3y=11
y=1

把y=1代入(1) ,可得
x=2(1)+5
=7


4.
3y-4x=14_________________(1)
y+2x=8___________________(2)

從(1) ,可得
3/2 y -2x=7__________________(3)

(2)+(3)
5/2 y=15
y=6

把y=6代入(2),可得
6+2x=8
2x=2
x=1