3A+3B=41 2A+4B=29

3A+3B=41 2A+4B=29
3A+3B=41 2A+4B=29

3A+3B=41 2A+4B=29
{3A+3B=41 　　①
2A+4B=29　　②
①×2,得
6A+6B=82 ④
②×3,得
6A+12B=87 ⑤
⑤-④,得
6B=5
∴B=5/6
把B=5/6代入①,得
3A+(5/2)=41
3A=77/2
A=77/6
∴原方程组的解是{A=77/6
B=5/6.

3A+3B=41 12A+12B=164
2A+4B=29 6A+12B=87

两式相减
12A-6A=164-87
6A=77
A=77/6

B=41/3-A=41/3-77/6=82/6-77/6=5/6

即a+b=41/3
b=41/3-a
代入
2a+164/3-4a=29
2a=77/3
a=77/6
b=41/3-a=5/6

3A+3B=41
2A+4B=29
A+B=41/3
A+2B=29/2
B=5/6
A=77/6

怎么

3A+3B=41 (1)
2A+4B=29 (2)
(1)-(2)得：
A-B=12
A=B+12
2（B+12）+4B=29
6B=5
B=5/6
A=B+12=77/6

A=77/6；
B=5/6；