00:01
In this question, we are asked to find the elementary matrix e, so that b equals to e times a.
00:10
Now, note that a and b are almost same, except for their first and second rows are interchanged.
00:21
All right.
00:22
Now, we want to find the matrix ae.
00:26
We want to find the matrix e, for which the matrix b equals to some matrix.
00:39
E multiplied by the matrix a.
00:59
And so here, well, let me move it to the next line.
01:19
So, and here we're going to place the matrix e.
01:26
All right.
01:28
Now, note that, we go that to multiply two matrices, we need to multiply the rows of the first matrix by the columns of the second matrix.
01:48
So for the matrix multiplication to be defined, so this means that each row of the matrix e must contain three entries.
02:00
Only in that case, a matrix multiplication is defined.
02:06
And to get three rows, the matrix must contain, matrix a must contain three rows, right? the resulting matrix must have three rows.
02:25
So a is going to be a three, e is going to be a three by three matrix...