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Câu hỏi: Với ${n}$ là số nguyên dương bất kì, ${n \geq 2}$, công thức nào dưới đây đúng?
A. ${A_n^2=\dfrac{(n-2) !}{n !}}$
B. $\text{A}_{\text{n}}^{\text{2}}\text{=}\dfrac{\text{2}!}{(\text{n-2})!}$
C. $\text{A}_{\text{n}}^{\text{2}}\text{=}\dfrac{\text{n}!}{\text{2}!(\text{n-2})!}$
D. ${ A_n^2=\dfrac{n !}{(n-2) !}}$
A. ${A_n^2=\dfrac{(n-2) !}{n !}}$
B. $\text{A}_{\text{n}}^{\text{2}}\text{=}\dfrac{\text{2}!}{(\text{n-2})!}$
C. $\text{A}_{\text{n}}^{\text{2}}\text{=}\dfrac{\text{n}!}{\text{2}!(\text{n-2})!}$
D. ${ A_n^2=\dfrac{n !}{(n-2) !}}$
${A_{n}^{2}=\dfrac{n !}{(n-2) !}}$
Đáp án D.