a) $\begin{vmatrix} -X & 1 &0 & ... &. \\ 0 & -X& 1& ... & 0\\ . & . & . & ... & .\\ 0 &0 & 0 & ... & 1\\ 1& 0 & 0 & ... &-X \end{vmatrix}$
b) $\begin{vmatrix} a_{1} -X& a_{2} & ... & a_{n}\\ a_{n}& a_{1}-X & ... & a_{n-1}\\ .& . & ... & .\\ a_{2}& a_{3} & ... &a_{1}-X \end{vmatrix}$