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Let $k$ be a field. Let $q=(x,y^2)$ be an ideal of $k[x,y]$.

What exactly does the notation $q=(x,y^2)$ mean, i.e. what kind of elements does $q$ contain? Is it the set of all elements $\alpha x + \beta y^2, \, \, \alpha, \beta \in k$?

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up vote 2 down vote accepted

The ideal $(x,y^2)$ consists of all elements of the form $\alpha(x,y) x + \beta(x,y) y^2$ for $\alpha, \beta \in k[x,y]$. More generally, if $R$ is a commutative ring and $f_1, \dots, f_k \in R$, then $(f_1, \dots, f_k)$ consists of all elements of the form $\alpha_1 f_1 + \cdots \alpha_k f_k$ with $\alpha_i \in R$.

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