$$ \begin{pmatrix} 0&1&1&-&1 \\ 1&0& a_{1}+a_{2} &-&a_{1}+a_{n}\\ 1&a_{2}+a_{1}&0&-&a_{2}+a_{n}\\ -&-&-&-&-\\ 1&a_{n}+a_{1}&a_{n}+a_{2}&-&0 \end{pmatrix} $$
I need to find a determinate, which looks like that.
Connected to my classes and methods that we use recently
probably I need to use matrix properties, The Gauss method.
I have tried to use them, but I don't find correct answer. It will be fine if I get a tiangle matrix or diagonal