Let $G$ be a finite group and $P$ be a Sylow 2-subgroup of $G$.
If at least one of maximal subgroups of $P$ is normal in $G$, then is $P$ cyclic?
Let $G$ be a finite group and $P$ be a Sylow 2-subgroup of $G$.
If at least one of maximal subgroups of $P$ is normal in $G$, then is $P$ cyclic?
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An easy counterexample . . .
Let $G=Z_2\times Z_2$.
Then $P=G$, and $P$ is not cyclic.
Since $G$ is abelian, every subgroup of $P$ is normal in $G$.