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# Matrix Determinents - +/- signs watch

1. when finding this determinant by cofactor expansion:

if i expand using column 1

^
^
do i use plus or minus 3?

and how do i know what to use in general with any matrix nxn

thanks
2. If the number you use is in the th row and th column then you multiply by ... so what do you think it should be? [This extends to the nxn case.]
3. (Original post by nuodai)
If the number you use is in the th row and th column then you multiply by ... so what do you think it should be? [This extends to the nxn case.]
ohhh ok so in this case i would use a minus because its in the 2nd row and 1st column and -1^3 = -1

thanks a lot!

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