prove that nPn =2. nPn-2
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nPn=n!/(n-n)!= n!/0!=n!
Other side =2.n!/(n-n+2)! =2.n!/2!=2.n!/2=n!
Hence they are equal as formula for nPn= n!/(n-n)!
Other side =2.n!/(n-n+2)! =2.n!/2!=2.n!/2=n!
Hence they are equal as formula for nPn= n!/(n-n)!
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