[Toán 11] Giải PT

N

niemkieuloveahbu

Đk: [TEX]x< y \in N[/TEX]

[TEX]PT \Leftrightarrow \frac{\frac{x+1)!}{(x-y)!}.(x-y)!}{(x-1)!}=72\\ \Leftrightarrow x^2+x-72=0\\ \Leftrightarrow x=8[/TEX]

PT có nghiệm [TEX] x=8, 7 \geq y \in N[/TEX]
 
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