Calculati: 5 [tex] C^{2}_{5} [/tex] - [tex] A_{5}^{2} [/tex]

E problema de Liceu , greseala mea :)


Răspuns :

[tex]C_5^2= \frac{5!}{2!*3!} = \frac{1*2*3*4*5}{1*2*1*2*3}= \frac{120}{12}=10 [/tex]
[tex]A_5^2= \frac{5!}{(5-2)!} = \frac{5!}{3!}= \frac{1*2*3*4*5}{1*2*3}= \frac{120}{6}=20 [/tex]
[tex]C_5^2-A_5^2=10-20=-10[/tex]