Determinant's value should be -15; I get 45; where am I going wrong?

Phatfoo

Phatfoo

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May 22, 2018
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This determinant doesn't work out I have tried this multiple times and can't see where I'm going wrong.

. . . . .\(\displaystyle M\, =\, \left|\begin{array}{rrrr}0&0&3&3\\3&0&1&2\\1&0&2&4\\2&1&3&2\end{array}\right|\)

The answer is apparently -15.

I can't get that answer. Where am I going wrong?

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Phatfoo said:
I have tried this multiple times and can't see where I'm going wrong.

View attachment 10407

The answer is apparently -15.

I can't get that answer. Where am I going wrong?

View attachment 10408
Click to expand...

When you evaluated the 2x2 determinants, you dropped a negative sign and a 3. Check that line carefully.

Also, you could have done a little less work by expanding at the first step by the second column rather than the first row. But that is not necessary.
 
Thank you for the fast help.

I see my error. I think I need fresh air. Too many numbers!
 
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