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4:41 PM
in Mathematics, 28 mins ago, by hyphen
https://math.stackexchange.com/questions/1090570/factorise-a-matrix-using-the-factor-theorem#comment6735204_1091452. Can anyone please answer this question? It's actually a comment on an answer.
in Mathematics, 28 mins ago, by hyphen
it's actually a comment
5
A: Factorise a matrix using the factor theorem

SaibalWhat you did is correct. But there is an easier way. Remember that for polynomial $p(x)$, if $p(a)=0$ then $(x-a)$ is a factor of $p(x)$. Denote the determinant by $\Delta$. It is obviously a polynomial in $x,\ y$ and $z$. Now, note that: $x=0\implies \Delta = 0$, so $x$ is a factor of $\Delta...

What about this matrix. $$\begin{vmatrix}? 1&1&1\\ x^2&y^2&z^2\\ x^3&y^3&z^3\\ \end{vmatrix}$$ x=1 is a factor by your method, but not really. — hyphen 33 mins ago
 
5:09 PM
in Mathematics, 8 mins ago, by hyphen
by mistake, I input the wrong det. Please give me a second.
in Mathematics, 3 mins ago, by hyphen
$$
\begin{vmatrix}
1&1&1\\
x^2&x^2&x^2\\
y^3&y^3&y^3\\
\end{vmatrix}$$
in Mathematics, 1 min ago, by Martin Sleziak
Isn't this determinant zero, regardless of the value of x, y?
in Mathematics, 1 min ago, by Martin Sleziak
Which also means that (x-1) divides that determinant.
in Mathematics, 1 min ago, by Martin Sleziak
Zero polynomial is divisible by any polynomial.
in Mathematics, 1 min ago, by Martin Sleziak
Still, this is an interesting question. (I am not really sure why we can use factorization in the post you linked.)
in Mathematics, 18 secs ago, by Martin Sleziak
I guess the asker was also somewhat confused by that - this seems basically as a follow-up question: factor theorem for multivariables.
I have to say, I'm not really sure why we can use the factorization in the way suggested in the linked post.
5
A: Factorise a matrix using the factor theorem

SaibalWhat you did is correct. But there is an easier way. Remember that for polynomial $p(x)$, if $p(a)=0$ then $(x-a)$ is a factor of $p(x)$. Denote the determinant by $\Delta$. It is obviously a polynomial in $x,\ y$ and $z$. Now, note that: $x=0\implies \Delta = 0$, so $x$ is a factor of $\Delta...

 
5:34 PM
So it seems that this was resolved in the main chatroom.
in Mathematics, 8 mins ago, by Thorgott
Diving multivariable polynomials is hard. The factor theorem in the form that is used still holds though. You can consider $K[X_1,...,X_n]$ as $K[X_1,...,X_{n-1}][X]$ and apply the usual factor theorem.
in Mathematics, 6 mins ago, by Martin Sleziak
The trouble with this argument is that $K[X_1,\dots,X_{n-1}]$ isn't a field.
in Mathematics, 5 mins ago, by Tobias Kildetoft
@MartinSleziak Well, still a UFD
in Mathematics, 5 mins ago, by Thorgott
The factor theorem works over all commutative rings.
in Mathematics, 3 mins ago, by Thorgott
If $f\in R[X],r\in R$ and $f(r)=0$, then $X-r$ divides $f$.
 

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