00:01
Section 3 .2, problem number 13, so we're dealing with determinants.
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So now we have a 5x5 matrix.
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We need to find the determinant of using elementary row operations to reduce it to upper triangular form.
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It means zeros below the diagonal.
00:18
Typically, i like to just clear it column by column.
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So if i'm going to clear column one and i'm going to use one number to do it, the best number to use is going to be that one.
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So i just, as a matter of practice, i like to put that at the very top of my matrix.
00:34
So let's switch row one with row two.
00:39
So that means this determinant will be minus.
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So let's just switch everything.
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1 -1, negative 1, 01.
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And then 3 -7, 1, 2, 3.
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Everything else remains the same.
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Minus 1 -66 -3709 -4 -8 -16 -negative -18 -12.
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So now we just go through several operations.
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So i'm going to put all of these sort of things together.
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So the operations i'm going to go through right now, i need to clear out.
01:25
So to clear out this three, that's going to be, what minus 3 row 1 plus row 2 to replace row 2.
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So row 1 remains the same.
01:43
1 -1 minus 1 -101.
01:48
And so now what happens is negative 3 times 1, negative 3 add to 3 you get 0.
01:54
Negative 3 times negative 1 is negative 3.
01:57
7 minus 3 would give you a 4.
02:03
Negative 3 times negative 1 is 3.
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3 plus 1 would be 4.
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4.
02:09
Negative 3 times 0 plus 2 is 2.
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And then negative 3 times 1 is negative 3.
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Add to 3 and you get 0.
02:20
Now if i want to clear out this 4, that's negative 4 row 1 plus row 3 to become the new row 3.
02:31
So negative 4 plus 4 is 0.
02:34
Negative 4 times 1 is negative 4.
02:36
8 minus 4 is 4.
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4 minus 1 is 3.
02:46
And then 4 times 0 plus 6 is 6.
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And then 4 times 1 is 4, 6 plus 4.
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So we have to this right.
02:57
So negative, sorry, it's negative 4.
03:00
Negative 4 times negative 1 is negative 4.
03:03
6 minus 4 is 2.
03:04
So 0, 4, 3, 6, 2.
03:08
And then to clear out this 3, that's minus 3 row 1 plus, 1, 2, 3, this is row 4 to become the new row 4.
03:20
So this gives me a 0.
03:24
Negative 3, so 7 minus 3 is 4.
03:28
And then negative 3 times negative 1 is 3.
03:32
3 plus 0 is 3.
03:35
Negative 3 times 0 plus 9.
03:39
Negative 3 times 1 is negative 3.
03:42
4 minus 3 is 1.
03:45
And then for this last row to clear that number, i'm going to have negative 8 times row 1 plus row 5 to become the new row 5.
03:59
So this gives me a 0.
04:01
Negative 8 times 1 is negative 8.
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16 minus 8 is 8.
04:06
Negative 8 times negative 1 is 8.
04:11
8 minus 1 is 7...