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combinari de 7 luate cate 2 . Vreau rezolvare amanuntita,pt.ca nu o inteleg.Multumesc

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Antonio9990
[tex]\displaystyle \boxed{\bold{C^k_n= \frac{n!}{k!(n-k)!} }} \\ \\ n!=1\cdot 2\cdot3 \cdot ... \cdot n \\ \\ C_7^2= \frac{7!}{2!(7-2)!}= \frac{\not7!}{2!\cdot\not5!} = \frac{6\cdot7}{2} = \frac{42}{2}=21 [/tex]