Question

сократить дробь n!/(n-3)!

Answer 1

$frac{1*2*3*...*(n-3)(n-2)(n-1)n}{1*2*3*...*(n-3)}= frac{(n-2)(n-1)n}{1}= n^{3}-3n^{2}+2n$

Answer 2

$frac{n!}{(n-3)!} = frac{(n-3)!*(n-2)*(n-1)*n}{(n-3)!} =(n-2)*(n-1)*n=$
$(n-2)*(n-1)*n=(n^2-n-2n+2)*n=(n^2-3n+2)*n=$
$=(n^2-3n+2)*n=n^3-3n^2+2n$