(Solved): (20pts) Find the inverse of a 3 by 3 upper triangular matrix U, with nonzero entries a,b,c,d,e,f. Y ...

(20pts) Find the inverse of a 3 by 3 upper triangular matrix $U$, with nonzero entries a,b,c,d,e,f. You could use cofactors and the formula for the inverse. Or possibly Gauss-Jordan elimination. of $U=?\begin{array}{lll}a& b& c\\ 0& d& e\\ 0& 0& f\end{array}?$ b) (10pts) Suppose the columns of $U$ are eigenvectors of a matrix A. Show that $\mathrm{A}$ is also upper triangular.