从第n-1行到第1行,每行减去下一行*α/β0 0 ... 0 0 β+α(-α/β)^(n-1)0 0 ... 0 β 0...0 β ... 0 0 0β 0 ... 0 0 α结果是:(-1)^(n(n-1)/2)(β^n+(-1)^(n-1)α^n)