Inverse of Matrix Sum

1. Apr 6, 2008

Physics_wiz

Does anyone know a formula for the inverse of a sum of two upper triangular matrices?

2. Apr 7, 2008

HallsofIvy

What makes you think there is such a formula?

Have you looked at the inverse of
$$\left(\begin{array}{cc}a & b \\ 0 & c\end{array}\right)+ \left(\begin{array}{cc}x & y \\ 0 & z\end{array}\right)$$?