有d數學問題想問下

a + 3b = 18 ------1
3a + 5b = 34 -----2

1. a = 18-3b

2. 3( 18-3b) + 5b = 34
54 - 6b + 5b = 34
54 -b = 34
b = 20

1. a = 18 - 3 ( 20 )
a = 42

2007-07-12 13:24:17 補充：
a + 3b = 18 ------1{3a + 5b = 34 -----2在1 , a = 18-3b在2 , 3 ( 18-3b) + 5b = 34 54 - 9b + 5b = 34 54 -4b = 34 b = 5代返b = 5 去1 , a = 18 -3b a = 18-3(5) a= 3岩岩打錯左少少．．．．要改返今次呢個先岩

對唔住.我唔知

a+3b=18--------1
{
3a+5b=34---------2
From 1,
a=18 - 3b----------3
Sub. 3 into 2
3(18 - 3b) +5b = 34
54 - 9b + 5b = 34
- 4b = - 20
b=5

Sub b=5 into 1
a+3(5)=18
a=3

2007-07-12 13:23:22 補充：
樓上計錯數