|a-b-c 2a 2a|
|2b b-a-c 2b|
|2c 2c c-a-b|
所有行加到第一行
=|a+b+c a+b+c a+b+c|
|2b b-a-c 2b|
|2c 2c c-a-b|
=(a+b+c)|1 1 1|
|0 -b-a-c 0|
|0 0 -c-a-b|
=(a+b+c)^3