Question

simplifique
a) n!/(n-2)!
b) 15!/2!5!
C) 20!/15!

Answer 1

Recordando: $n!=n.(n-1).(n-2)...1$

$\frac{n!}{(n-2)!}\\\\\frac{n.(n-1).(n-2)!}{(n-2)!}\\\\n(n-1)$

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$\frac{15!}{2!5!}\\\\\frac{15.14.13.12.11.10.9.8.7.6.5!}{2!5!}\\\\15.14.13.12.11.10.9.8.7.3=5448643200$

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$\frac{20!}{15!}\\\\\frac{20.19.18.17.16.15!}{15!}\\\\20.19.18.17.16\\\\1860480$