C₄¹ ( combinari de 4 luate cate 1) = [tex] [tex] \frac{n!}{k!(n-k)!} [/tex] = [tex] \frac{4!}{1!(4-1)!} [/tex] = [tex] \frac{4!}{1!3!} [/tex] = [tex] \frac{3!4}{3!1} [/tex][tex] \frac{4}{1} [/tex] = 1
Nota= 1!=1; 2!=1·2; 3!=1·2·3; 4!=1·2·3·4; 5=1·2·3·4·5; etc
C₃² + C₇⁵ (Combinari de 3 elem. luate cate 2 + combinari de 7 elem. luate cate 5) =[tex] \frac{3!}{2!1!} + \frac{7!}{5!2!}[/tex] = [tex] \frac{2!3}{2!.1} + \frac{5!.6.7}{5!.2} = \frac{3}{1} + \frac{42}{2} = 3+21=24[/tex]
