Question

Calculati: 5 $C^{2}_{5}$ - $A_{5}^{2}$

E problema de Liceu , greseala mea :)

Answer 1

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