按第1行展开：
| c d 0| | 0 c d |
=a| e f 0| -b|0 e f |
| 0 0 h| |g 0 0 |
| c d| | c d|
=ah| e f |-bg| e f |
=ah(cf-de)-bg(cf-de)
=(cf-de)(ah-bg)