[Toán đại 8] Tìm $x^n$

H

huongmot

$3x^{n-1}(x^{n+1}+y^{n+1})-3x^{n-1}y^{n+1}=27$
$\rightarrow 3x^{n-1}(x^{n+1}+y^{n+1}-y^{n+1})=27$
$\rightarrow 3x^{n-1}x^{n+1}=27$
$\rightarrow 3x^{2n}=27$
$\rightarrow x^{2n}=9$
Ta thấy: $9=3^2$
$\rightarrow x=3; 2n=2 \leftrightarrow n=1$
$\rightarrow x^n=3^1=3$
 
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