# Matrix i dont understand

• Nov 24th 2012, 02:07 AM
Petrus
Matrix i dont understand
Its on swedish but its a example i dont understand i dont understand how they got 208... I dont understand what method they use!:S
• Nov 24th 2012, 03:42 AM
BobP
Re: Matrix i dont understand
A determinant can be expanded along any row or down any column by adding together the products of each element in the row or column with their respective cofactors. In the example you show, the third column has been chosen because one of the elements is zero and that simplifies the arithmetic.
And by the way, they've made a mistake. The first bracket should be (28 + 10) and not (28 + 12).
• Nov 24th 2012, 03:46 AM
Petrus
Re: Matrix i dont understand
Yeah thats what i thought same... I was like 12?!?! Now evrything is Clear! I love that i bought a book that i have fined 3-4 wrong on it even a formula was wrong!! Goosh i hate it and ty alot!
• Nov 24th 2012, 03:50 AM
Petrus
Re: Matrix i dont understand
Wait shall it not be (28-10)?? 5•-2=-10??
• Nov 24th 2012, 06:30 AM
topsquark
Re: Matrix i dont understand
Quote:

Originally Posted by Petrus
Wait shall it not be (28-10)?? 5•-2=-10??

$\left | \begin{matrix} a & b \\ c & d \end{matrix} \right | = ad - bc$

Note the extra "-" on the bc term.

-Dan
• Nov 24th 2012, 06:38 AM
Petrus
Re: Matrix i dont understand
Ty alot dan! Really explained well and now i understand this ty alot