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Results tagged with polynomials
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user 12031
Questions in which polynomials (single or several variables) play a key role. It is typically important that this tag is combined with other tags; polynomials appear in very different contexts. Please, use at least one of the top-level tags, such as nt.number-theory, co.combinatorics, ac.commutative-algebra, in addition to it. Also, note the more specific tags for some special types of polynomials, e.g., orthogonal-polynomials, symmetric-polynomials.
14
votes
When does 'positive' imply 'sum of squares'?
+1 - 3 x^2y^2$$
which can be written as a sum of four (even three) rational squares
$$ \frac{x^2y^2(x^2 + y^2 -2)^2(x^2 + y^2 +1) +(x^2 - y^2)^2}
{(x^2 + y^2)^2},$$
yet is not a sum of squares of polynomials …