Solution
= Solution
Let $e_{ij}$ denote the <matrix unit> with one at position $(i,j)$ and zero elsewhere. The five inverses are
$$
\boxed{E_1^{-1}=I+e_{21},\quad E_2^{-1}=I+2e_{31},\quad E_3^{-1}=I-e_{41},\quad E_4^{-1}=I+e_{32},\quad E_5^{-1}=I-e_{42}.}
$$
Thus each is the <identity matrix> with only the indicated <off-diagonal matrix entry> altered. These inverses reverse the corresponding row additions; no row scaling or permutation is involved.