More specifically: Let $V$ be an $n$ dimensional vector space over a finite field $F_{q}$. Let $S\subset V$ be a $k$-dimensional ($k> 1$) subspace. Does there exist an $m$-dimensional subspace $W\subset V$, with $m=\dim(W)>1$ such that $\dim(S\cap W)=1$?
2026-05-05 18:47:27.1778006847
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Intersection of subspaces: Does there exist for a subspace a non trivial subspace such that that their intersection has dimension 1?
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it is impossible because of the assumption which is $W\subset V$
$W\subset V \Rightarrow W \cap V=W$
$W \cap V=W \Rightarrow dim(W \cap V)=dim(W)>1$ which means $dim(W) \neq1$
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Given a vector basis of V, and considering the subbasis that spans the subspace $S$ (S is not all V) then it is enough to take the basis of V, and substract all the vectors except 1 of those that span $S$ (considering the subbase for $S$ formed by vectors of the base for $V$). Then the resulting spanned subspace is the $W$ i have been looking for. It is clear that $W$ is not unique.
Hint. Let $T$ be the span of $S$ and $W$. Then $$ \dim(T) = \dim(S) + \dim(W) - \dim(S \cap W) $$
Whenever you can satisfy this equality there will be such a $W$.
The fact that the field is finite is irrelevant.