Linear Algebra- Find Elementary Matrix E such that EA=B

These are my lecture for University and College level students.

[pranoyshaji]

how can state that 'E' is invertible ? can u please explain it ?

[hissaanali]

she choose the worse example. i know what an elementary matrix is. would have been better if she could have told us more about how to solve it when it's not a special case like in this example.