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July 24th, 2019, 04:51 AM   #1
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Calculate a determinant

How could i calculate determinant this matrix. if it doesn't have exact dimension
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July 24th, 2019, 06:00 AM   #2
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Originally Posted by mathodman25 View Post
How could i calculate determinant this matrix. if it doesn't have exact dimension
The central diagonal {(i,i)} has the product $\displaystyle (a+b)^N$. This is a "positive" diagonal. For a 3x3 or higher, all other diagonals have at least one zero in them. (Note, the "1"s diagonal has the zero from (1,N) and the "ab"s diagonal has the zero from (N,1). All the down-and-to-the-left diagonals also have at least one zero.) The determinant should be $\displaystyle (a+b)^N \forall N \geq 3$, where N is the size of the matrix. Try it for 3x3 and 4x4 to test it. Happens to work for 1x1, also. 2x2 would be a special case.
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July 24th, 2019, 07:47 AM   #3
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Scratch the above answer. It's wrong, and for some reason I can't edit it.

Solved it by example (up to 5x5):
$\displaystyle |2 \times 2| = a^2 + ab + b^2$
$\displaystyle |3 \times 3| = a^3 + a^2b + ab^2 + b^3$
$\displaystyle |N \times N| = \sum_{i=0}^{N} a^ib^{N-i}$

Last edited by DarnItJimImAnEngineer; July 24th, 2019 at 08:13 AM.
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