[tex]A_5^3-4\cdot C_6^2=5\cdot4\cdot3-4\cdot\dfrac{6\cdot5}{1\cdot2}=60-60=0[/tex]
Am folosit formula [tex]A_n^k=n(n-1)(n-2)...(n-k+1)[/tex] (se retine si se aplica usor, pentru ca in partea stanga sunt exact k numere.)
Si [tex]C_n^k=\dfrac{n(n-1)(n-2)...(n-k+1)}{k!}[/tex]
