副对角线上边元素全是0的行列式计算,初学线代,有点迷茫,-1的次数就是算不对
|0...00A1n|
|0...0A2,n-1A2n|
|0...A3,n-2A3,n-1A3n|
|..............|
|An1...An,n-2An,n-1Ann|