Ludium - Learn by Doing

Your summary note

1. Building a permutation matrix from the identity
  State that performing the wanted row swap on the identity produces $P$ , and write the $2 \times 2$ matrix with ones off the diagonal that exchanges rows one and two.
2. The inverse $E^{-1}$ with $E^{-1}E = I$
  Give the definition of the inverse as the matrix that undoes $E$ , and write $E^{-1}$ for the step subtracting $3$ times row one from row two, with $+3$ in place of $-3$ .
Attempt 1 of 2