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Let $G$ be a finite group, $H$ and $K$ subgroups of $G$ such that $G=HK$. Show that there exists a $p$-Sylow subgroup $P$ of G such that $P=(P\cap H)(P\cap K)$.

I looked at the proof here, but I can't understand step "(3) It is clear in this situation that $P=(P\cap H)(P\cap K)$." Help.

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    |G|/ |(P∩H)(P∩K)|=(|H||K||P∩H∩K|)/(|P∩H||P∩K||H∩K|) is not divisible by$p$==>|(P∩H)(P∩K)| is the largest p power that divides the order of G. Thank you very much.2012-04-01

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