Question

помогите решить 21!/3!•18!​

Answer 1

$boxed {; (n+1)!=n!, (n+1); }\\frac{21!}{3!, cdot 8!}=frac{8!, cdot , 9cdot 10cdot ...cdot 21}{3!, cdot , 8!}=frac{9cdot 10cdot ,,,cdot 21}{2, cdot , 3}=\\=underbrace {3cdot 5cdot 11cdot 12cdot 13cdot 14cdot 15}_{5405400}cdot underbrace {16cdot 17cdot 18cdot 19cdot 20cdot 21}_{39070080}$