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Published online by Cambridge University Press: 11 September 2025
This note provides an alternative proof of a theorem by Li et al. [‘On the primitivity of some trinomials over finite fields’, Adv. Math. (China) 44(3) (2015), 387–393] regarding the nonprimitivity of the trinomial $x^{n}+ax+b$ over
$\mathbb {F}_{q^{m}}$ under the condition
$a^{n}b^{1-n}\in \mathbb {F}_{q^{u}}^{\ast }$ for some positive integer
$u<m$. We extend this result to the trinomial
$x^{n}+a^{k}x^{k}+b^{k}$, showing its nonprimitivity over
$\mathbb {F}_{q^{m}}$ when
$ a^{n}b^{k-n}\in \mathbb {F}_{q^{u}}^{\ast }$ for some positive integer
$u<m$. While the existing proof relies on the theory of linear recurrences over finite fields, our approach is short and self-contained, requiring no prior knowledge of this area.