Talk:Multiplicative inverse

Error in proof

In the "Further Remarks" section, the proof has a small error: the third line which says "=> a^(-1).a.(x-y)=0" should be deleted: the proof is supposed to show that a^-1 exists, so we can't use it in the proof. We can skip directly from line 2 to line 4 since a is not a zero divisor.

Oli —Preceding unsigned comment added by 87.194.173.194 (talk) 14:27, 4 January 2010 (UTC)

Reciprocals of Irrationals

I stumbled across the fact that there are an infinite number of reciprocal pairs that share mantissas (meaning they are separated from their reciprocals by an integer). I thought it was worthy of inclusion. In fact, I haven't been able to find any information that this had already been discovered, but I don't really think I was the first. I'm also curious if the formula I found for identifying them, finds all such pairs. Can anyone direct me to a text or other source where this fact had already been discussed? I would appreciate reading more about it. Lyleq (talk) 03:13, 17 October 2010 (UTC)

If $x-{\frac {1}{x}}=n,$

then, by the quadratic formula, $x={\dfrac {n}{2}}\pm {\sqrt {\left({\dfrac {n}{2}}\right)^{2}+1}}.$

If n is even, that reduces to the formula you have. — Arthur Rubin (talk) 08:08, 18 October 2010 (UTC)

Left and right multiplicative inverses ?

Are there systems where one has to consider different left and right multiplicative inverses?

If the product rule is associative, it's easy to see that the two have to be the same -- eg, if p and q are the left and right multiplicative inverses of a respectively, then associativity would seem to imply that

(pa)q = p(aq)

so

q = p

The two still turn out to be the same if the algebra is not associative, but it is alternative, such as the octonions. (Demonstration, anyone?)

I'm not sure whether the equivalence still holds for power associative algebras like the sedenions.

Does it hold generally for algebras constructed using the Cayley-Dickson construction (not necessarily starting with complex numbers and quaternions, but also starting with different associative algebras) ?

What can be said about the conditions for the right inverse and left inverse to be equivalent?

Is this something the article should discuss? Jheald (talk) 18:21, 16 September 2011 (UTC)

Terminology

The article would do well to discuss why the convoluted terminology 'multiplicative inverse' is preferred to 'reciprocal', even as early as the seventh grade: https://s.yimg.com/hd/answers/i/3659d3369ebb4c4da9e17b1fb09b8d13_A.jpeg?a=answers&mr=0&x=1393291657&s=b8efbedb4fe036d7d231d0a0d08b5b8b

I see that there was in 2007 a stub article 'reciprocal' which might have dealt with this point.

81.132.145.184 (talk) 23:39, 24 February 2014 (UTC)

constant "e"

Thsi equation has the right properties to be used in a graphical explanation of "e" --Backinstadiums (talk) 12:48, 24 February 2020 (UTC)