So the row operations I was given are :

1) E2 => -2E2

2)E1 <-> E3



So i did calculate the determinant of matrix B as 6


But i really cant find any resource on how det(B) relates to det(-B). That's where I am having issues. I know that [-B] is the negation of all the elements in [B], but I am having a hard time joining that with the concept of determinants. I couldn't find any examples online about this either. Nor does my textbook have anything that seems helpful.

  • $\begingroup$ What do you denote E1, E2, &c.? $\endgroup$
    – Bernard
    Mar 24 '20 at 18:00
  • $\begingroup$ that's the row operations. that's how they were denoted on the question. I was also confused as usually they are denoted by R1 or R2. $\endgroup$
    – p.nish
    Mar 24 '20 at 18:01

If $B$ is a $n\times n$ matrix then $\rm{det} (-B)=(-1)^n\rm{det} (B)$, you can see this using the definition of determinant that takes n elements of the matrix, multiplies them and sum them following the permutation form, if all of them change by -1 then all the elements of the sum will change by (-1)^n factor.

  • 1
    $\begingroup$ omg . I cant belive i didnt see that. Thank you $\endgroup$
    – p.nish
    Mar 24 '20 at 18:04
  • $\begingroup$ You are welcome. $\endgroup$
    – Camilo160
    Mar 24 '20 at 18:05

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