∴
| b |
| a |
| a |
| b |
| c |
| a |
| a |
| c |
| c |
| b |
| b |
| c |
∴
| b |
| a |
| a |
| b |
| c |
| a |
| a |
| c |
| c |
| b |
| b |
| c |
三式相加得，
| b |
| a |
| c |
| a |
| c |
| b |
| a |
| b |
| a |
| c |
| b |
| c |
∴(
| b |
| a |
| c |
| a |
| c |
| b |
| a |
| b |
| a |
| c |
| b |
| c |
即
| b+c−a |
| a |
| a+c−b |
| b |
| a+b−c |
| c |
| b+c−a |
| a |
| a+c−b |
| b |
| a+b−c |
| c |
| b |
| a |
| a |
| b |
| c |
| a |
| a |
| c |
| c |
| b |
| b |
| c |
| b |
| a |
| a |
| b |
| c |
| a |
| a |
| c |
| c |
| b |
| b |
| c |
| b |
| a |
| c |
| a |
| c |
| b |
| a |
| b |
| a |
| c |
| b |
| c |
| b |
| a |
| c |
| a |
| c |
| b |
| a |
| b |
| a |
| c |
| b |
| c |
| b+c−a |
| a |
| a+c−b |
| b |
| a+b−c |
| c |