Let $k$ be a field and consider the ideal $I=(x,y) \subset k[x,y]$. Am I correct in saying that $(x,y)/(x,y)^{2}$ is generated as a $k$-vector space by the class of $x$ and $y$?
$k$-basis of a quotient of ideals in polynomial ring
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abstract-algebra
1 Answers
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Yes. We have that $(x,y)=\{f\in k[x,y]\mid f \text{ has no terms of degree}\leq0\}$
and that $(x,y)^2=(x^2,xy,y^2)=\{f\in k[x,y]\mid f \text{ has no terms of degree}\leq1\}$
so that any $f\in(x,y)$ is equivalent modulo $(x,y)^2$ to one having terms only in degree 1, i.e. an element of $(x,y)$ of the form $ax+by$.