00:01
In this problem, we're given this set of matrices, these three matrices right here, i've written them down for us, and we're asked to determine by row operations how we got the numbers in the boxes and what they are.
00:24
So in other words, as we went from this first matrix down to the second matrix, and then the second matrix down to the third matrix, how we got the answers in the boxes.
00:38
Okay, so first of all, let's start with going from the second to the third matrix.
00:46
The first row, we can see that it starts with a 1, right? and no other rows have a 0 in the first column.
00:58
So there's nothing that we could add to the first row.
01:03
Couldn't add anything from row 2 or row 3 to get, what's in this this first row in the third matrix.
01:13
So that means these numbers in this first row must have been the same in that second matrix.
01:20
So that means that this first box right here is a two, this is a four, and this is a three over two, a three halves.
01:32
Okay? now, the question is, how do we get from the second, row there in the second matrix down to the second row in the bottom matrix well i went from the first entry here i went from 1 to a 0 so i must have subtracted 1 somehow and the first row would let me subtract 1 so if i take row 2 minus row 1 then then i get a 0 in the first entry okay, so the minus two, i'm sorry, minus one, minus two, that's a minus three.
02:37
So i have a minus three here that shows up then, don't i? okay, and let's just check.
02:44
If i take minus three, minus four, that gives me minus seven, so that checks.
02:50
If i take two minus three halves, well, three halves is one and a half.
02:57
So two minus one and a half, that's a half.
02:59
So that checks as well.
03:02
Okay, so now the question is, how do i get to the third row here? from a 2 to a 0, right? looking at that entry right there...