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[tex]C_{6} ^{2}[/tex] - [tex]A_{4} ^{2}[/tex]

Răspuns :

[tex]$C^{k}_{n} = \frac{n!}{k!(n-k)!}, \text{ } A^{k}_{n} = \frac{n!}{k!}$[/tex]

[tex]$C^{2}_{6} - A^{2}_{4} = \frac{6!}{2! \cdot 4!} - \frac{4!}{2!} = \frac{6 \cdot 5 \cdot 4!}{2! \cdot 4!} - \frac{4\cdot 3 \cdot 2!}{2!} = 15 - 12 = \boxed{3}$[/tex]