What is the determinant of the matrix:
⎝ ⎜ ⎜ ⎜ ⎜ ⎜ ⎛ 1 2 0 1 6 2 2 0 1 6 3 2 0 1 6 ⋮ 2 0 1 8 2 0 1 6 2 2 0 1 6 3 2 0 1 6 4 2 0 1 6 ⋮ 2 0 1 9 2 0 1 6 3 2 0 1 6 4 2 0 1 6 5 2 0 1 6 ⋮ 2 0 2 0 2 0 1 6 … … … … 2 0 1 8 2 0 1 6 2 0 1 9 2 0 1 6 2 0 2 0 2 0 1 6 ⋮ 4 0 3 5 2 0 1 6 ⎠ ⎟ ⎟ ⎟ ⎟ ⎟ ⎞
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In fact, this solution generalizes immediately to any n × n matrix where the ( i , j ) term is ( a i + b j − 1 ) m with m ≤ n − 2 . This can produce interesting results, esp when we have variables / fractions.
E.g What is the determinant of the matrix:
⎝ ⎛ 2 x x + y x + z x + y 2 y y + z x + z y + z 2 z ⎠ ⎞
It is not immediately obvious that the rows are linearly independent, but since we know the determinant is 0, hence they are!
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Indeed, except I think you mean ( n + 1 ) × ( n + 1 ) matrix, or else m ≤ n − 2 .
Sir @Mark Hennings I couldn't get how the set of polynomials form a linearly independent collection.Can you please explain in more details.
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The vector space of polynomials of degree at most n − 1 has dimension n (the monomials 1 , x , x 2 , ..., x n − 1 form a basis, for example). Since there are n + 1 polynomials in the collection x n − 1 , ( x + 1 ) n − 1 , ..., ( x + n ) n − 1 , they must be linearly dependent (basically, by the definition of what dimension is).
General results tell us that
Together, these results tell us that the dimension of a finite-dimensional vector space is well-defined (two bases have the same number of elements), and that any linearly independent set cannot have more elements than the dimension of the vector space. It is this last result that I am using.
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For any n ≥ 2 the collection of polynomials x n − 1 , ( x + 1 ) n − 1 , ( x + 2 ) n − 1 , . . . , ( x + n ) n − 1 form a set of n + 1 polynomials in the n -dimensional vector space of polynomials of degree at most n − 1 . Thus they form a linearly dependent collection, and so there exists a collection of constants a 0 , a 1 , a 2 , . . . , a n (not all zero) such that F ( x ) ≡ a 0 x n − 1 + a 1 ( x + 1 ) n − 1 + a 2 ( x + 2 ) n − 1 + . . . + a n ( x + n ) n − 1 ≡ 0 If A ( n ) is the ( n + 1 ) × ( n + 1 ) matrix A ( n ) i , j = ( i + j − 1 ) n − 1 1 ≤ i , j ≤ n + 1 then A ( n ) ⎝ ⎜ ⎜ ⎜ ⎛ a 0 a 1 ⋮ a n ⎠ ⎟ ⎟ ⎟ ⎞ = ⎝ ⎜ ⎜ ⎜ ⎛ F ( 1 ) F ( 2 ) ⋮ F ( n + 1 ) ⎠ ⎟ ⎟ ⎟ ⎞ = 0 and hence the matrix A ( n ) is singular, and has determinant 0 . In this case, we see that A ( 2 0 1 7 ) has determinant 0 .