if you look at the wolframalpha calculation page:

-13-26i - Wolfram|Alpha

it factorises -13-26i as

i×(1+2 i)×(2+3 i)×(3+2 i)

my question is why is theia necessary factor to take out? are the rules regarding this?

Thanks

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- Oct 4th 2011, 03:57 AMwalleyegaussian prime factorisation
if you look at the wolframalpha calculation page:

-13-26i - Wolfram|Alpha

it factorises -13-26i as

i×(1+2 i)×(2+3 i)×(3+2 i)

my question is why is the**i**a necessary factor to take out? are the rules regarding this?

Thanks - Oct 4th 2011, 04:40 AMTKHunnyRe: gaussian prime factorisation
Hint: (1-i) is NOT a Gaussian Prime. It can be factored: i(1+i)

- Oct 6th 2011, 07:59 PMroninproRe: gaussian prime factorisation
I don't think that this is correct. There is a characterisation of Gaussian primes that says that a Gaussian integer is prime if and only if one of the conditions is true:

- Its norm is prime (as an integer)
- It is a prime (as an integer) of the form $\displaystyle 4k+3$

In this case, the norm of $\displaystyle 1-i$ is $\displaystyle 1^2+(-1)^2=2$, which is prime. So $\displaystyle 1-i$ is prime.

The issue that should be brought up is that unique factorisation only holds*up to a unit*(i.e. invertible number). For example, normal integer factorisation follows this idea: $\displaystyle 25=5\times 5$ or $\displaystyle 25=(-5)\times (-5)$. In the second example, we have multiplied the factors by $\displaystyle -1$ (which is invertible), but we do not consider it to be inherently different from the first. So in this case, $\displaystyle 1-i$ only differs from $\displaystyle 1+i$ by multiplying by the unit $\displaystyle i$, which is no difference at all, as far as unique factorisation goes.

So to address original question, throwing in $\displaystyle i$ is analogous to repeatedly multiplying by $\displaystyle -1$ with the usual integer factorisation. If it bothers you, you may let one of the terms absorb it. - Oct 6th 2011, 09:26 PMTKHunnyRe: gaussian prime factorisation
I'm making stuff up again?! Only explanation I could think of for the question presented. It's -i, anyway. Wow. Taking a break...

- Oct 6th 2011, 09:38 PMroninproRe: gaussian prime factorisation
No worries! Mistakes happen.