Timeline for A question about involutions and polynomials
Current License: CC BY-SA 3.0
4 events
| when toggle format | what | by | license | comment | |
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| Jan 22, 2017 at 8:23 | comment | added | Pietro Majer | @stackExchangeUser if you really need to make the answer into a concrete construction, you need a bijection $(a,b)\leftrightarrow(a',b')$ between rational pairs $(a,b)$ s.th. $a^2-4b$ is a square and rational pairs $(a',b')$ s.th. $a'^2-4b'$ is not a square. There should be an explicit such bijection, playing with prime factorization, although not particularly nice or simple. A warm-up should be: finding an involution of $\mathbb{Q }$, $q\leftrightarrow q'$ such that $q$ is a square iff $q'$ is not. | |
| Jan 22, 2017 at 8:10 | comment | added | user6671 | Nice argument, with the countability! | |
| Jan 22, 2017 at 8:08 | vote | accept | CommunityBot | ||
| Jan 22, 2017 at 7:37 | history | answered | Fedor Petrov | CC BY-SA 3.0 |