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anonymous
 one year ago
Need help with determinants of matrix. Question is in the attached file
anonymous
 one year ago
Need help with determinants of matrix. Question is in the attached file

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anonymous
 one year ago
Best ResponseYou've already chosen the best response.0So my question is can I just take the cofactor expansion of column 3. which will give me dw:1444515136849:dw right?

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0at the end is just a question mark, its not part of the solution

amistre64
 one year ago
Best ResponseYou've already chosen the best response.5i cant remember how to express the alternating (1)^n in terms of the element picked from the ith row and jth column ...

amistre64
 one year ago
Best ResponseYou've already chosen the best response.5+  +  +   +  +  + +  +  +  visually it is compiled like this

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0I dont know what that means

amistre64
 one year ago
Best ResponseYou've already chosen the best response.5oh well, there was some 'summation' formula that is compact for it ... which element are we getting the cofactor expression for?

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0in the question it just says to get the determinant using cofactor expansion

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0so in the question I took the cofactor expansion of the 3rd column and I got what is in the drawing

amistre64
 one year ago
Best ResponseYou've already chosen the best response.5http://www.wolframalpha.com/input/?i=cofactor+expansion it appears that you followed the formula correctly to me 1^(3+2) (7) .. yeah you did fine for that element

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0So now I just have to get a cofactor expansion of any aij entry in the 3x3 matrix correct? so I took the a31 entry dw:1444516001995:dw is that right?

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0dw:1444516084912:dw

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0but when I check my answer on determinant calculator its totally off

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0what am i doing wrong?

mathmate
 one year ago
Best ResponseYou've already chosen the best response.0One good trick to remember, diagonal is always positive! Yes, 3 column is best!

amistre64
 one year ago
Best ResponseYou've already chosen the best response.5\[...+(1)^{(3+3)}~(7)[... +(1)^{(3+1)}~(1) \begin{pmatrix} 7&10\\ 3&8 \end{pmatrix} +... ]+...\]

amistre64
 one year ago
Best ResponseYou've already chosen the best response.5you have one more cofactor to express

amistre64
 one year ago
Best ResponseYou've already chosen the best response.5unless you simply stopped at this and decided to shortcut the 2x2 det

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0yes that what I tried to do

Empty
 one year ago
Best ResponseYou've already chosen the best response.0Yeah you were able to throw away those other 3 determinants with your first step since you had 3 zeroes there, but now you don't have anymore zeroes so you have to fully evaluate the ones that are rest

amistre64
 one year ago
Best ResponseYou've already chosen the best response.5oh, i thought they were just randomly checking an element in the expansion .... didnt even consider that they were thinking this was the whole of it

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0@empty so from when I have the 3x3 det in the second step. I have to get the cofactor expansion of each row or column? is that what you are trying to say?

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0*sorry not "each" row, just one row or column

amistre64
 one year ago
Best ResponseYou've already chosen the best response.5we only need to go across one row right? \[\begin{pmatrix} a&b\\c&d \end{pmatrix}\] row 1 \[(1)^{(1+1)}(a)(d)+(1)^{(1+2)}(b)(c)=adbc\] or row2 \[(1)^{(2+1)}(c)(b)+(1)^{(2+2)}(d)(a)=adbc\]

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0yes, one row or one column

mathmate
 one year ago
Best ResponseYou've already chosen the best response.0dw:1444517082554:dw It's a personal preference, but I prefer to expand along the first column (because of the one's).

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0ok lets try that, let me do it on paper first

amistre64
 one year ago
Best ResponseYou've already chosen the best response.5a 3x3 has a diagonalized shortcut similar to the 2x2 .. you just have to copy the first 2 columns

amistre64
 one year ago
Best ResponseYou've already chosen the best response.5(gfc+hga+ieb) a b c a b e f g e f g h i g h +(afi+bgg+ceh)

amistre64
 one year ago
Best ResponseYou've already chosen the best response.5lol, forgot how to do the alphabet on that one ...

amistre64
 one year ago
Best ResponseYou've already chosen the best response.5hij for the bottom row of course .. and then corrected for lack of any common sense

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0dw:1444517589850:dw

anonymous
 one year ago
Best ResponseYou've already chosen the best response.070(30+24)(70+30)+(5630)=3706

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0that is still now right, according to a determinant calculator. can anyone see what I did wrong?

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0well igtg for now, ill leave this question open for anyone else to figure it out.

mathmate
 one year ago
Best ResponseYou've already chosen the best response.0@m0j0jojo I suggest you multiply by 7 at the very end, then there will be less distribution to do. so the whole thing, instead of: 70(30+24)(70+30)+(5630) should read: 7(10(30+24)1(70+30)+1(5630)) and you should get the correct answer (just a touch below 4300).

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0oh right, lol totally forgot about bedmas here. Thanks for the help!
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