Answer
$n=2$
Work Step by Step
$4·~_{n+1}P_2=~_{n+2}P_3$
$4~\frac{(n+1)!}{(n+1-2)!}=\frac{(n+2)!}{(n+2-3)!}$
$4=\frac{(n+2)!~(n+1-2)!}{(n+1)!~(n+2-3)!}=\frac{(n+2)(n+1)!~(n-1)!}{(n+1)!~(n-1)!}$
$4=n+2$
$n=2$
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