1. Finding The Determinant

I need to find the determinant of the matrix

2 -1 3
1 4 -2
-1 0 1

by the 3rd row.

I ended up getting -1(2-12) - 1(8+1) = 10 - 9 = 1

Is this correct?

2. Originally Posted by TreeMoney
I need to find the determinant of the matrix

2 -1 3
1 4 -2
-1 0 1

by the 3rd row.

I ended up getting -1(2-12) - 1(8+1) = 10 - 9 = 1

Is this correct?
Where did the -sign in front of 1(8+1) come from? (or to put it another
way it should be +).

You could check this yourself by expanding by the first row.

RonL

3. when i did expanded by the first row, i got 17.

2(4) -1(3) + 3(4) = 8 - 3 + 12 = 17.

Does it make a difference if you expand by a different row? because the problem says to expand by the 3rd row. When i did it again I ended up getting -1. I don't get it.

4. Originally Posted by TreeMoney
when i did expanded by the first row, i got 17.

2(4) -1(3) + 3(4) = 8 - 3 + 12 = 17.

Does it make a difference if you expand by a different row? because the problem says to expand by the 3rd row. When i did it again I ended up getting -1. I don't get it.
No it should be the same however you expand it, When I expand by the
first row I get:

2(4) - (-1)(1-2)+3(4) = 8 - 1 +12 =19.

When I expand about the last row I get:

-1(2-12) - 0(4-3) + 1(8+1) = 10 + 9 = 19

RonL

5. I figured out what i was missing. The negative sign in front of the first 1 in the last row. I must have missed it when i was copying things over. Thanks!!!!!