00:02
We want to know if b is a linear combination of the columns of a.
00:10
So that means that there's basically column vector x such that ax equals b.
00:24
So the question is, does x exist? so an easy way to figure that out is to take the determinant of a, and it turns out that that's non -zero.
00:39
But that doesn't really answer our question.
00:42
We have four multiple choice possibilities here.
00:46
We want to know which one of them is correct, and just taking the determinant won't answer that.
00:53
So we're supposed to use gaussian elimination.
00:56
So we make the augmented matrix that looks like this, where we put b as the fourth column of our matrix.
01:24
And then we want to reduce it using row operations.
01:30
This is actually pretty easy to do for this one.
01:34
So if i take, leave the first two rows alone, then i'm going to take the last row and then subtract three times the first row.
01:45
The goal is to put a zero in the lower left -hand corner.
01:52
So we get 3 minus 3 times 1...