Corrigé du 79 P. 44

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\[\begin{aligned} A &= 1\times 2 \times \cdots \times 14 = 14!.& \\ B &= 15\times \cdots \times 25& \\ &=\frac{{\color{Red}1\times 2 \times \cdots \times 14}\times 15\times \cdots \times 25}{{\color{Red}1\times 2\times \cdots \times 14}}& \\ &=\frac{25!}{14!}.& \\ C &= \frac{14\times \cdots \times 18}{1\times \cdots \times 5}& \\ &=\frac{{\color{Red}1\times \cdots \times 13}\times 14\times\cdots\times 18}{{\color{Red}1\times \cdots\times 13}\times 1\times \cdots\times 5}& \\ &=\frac{18!}{13!\times 5!}.& \end{aligned}\]

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