7^n+7^n+1+5^n+2=399
Consider ca ecuatia trebuia scrisa asa:
7^(n) + 7^(n+1) + 7^(n+2) = 399
Rezolvare:
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[tex]\displaystyle\bf\\7^{n} + 7^{n+1} + 7^{n+2} = 399\\\\Dam~factor~comun~pe~7^n.\\\\7^n\Big(7^0+7^1+7^2\Big)=399\\\\7^n\Big(1+7+49\Big)=399\\\\57\times7^n=399\\\\7^n=\frac{399}{57}\\\\7^n=7\\\\7^n=7^1\\\\\implies~\boxed{\bf n=1}[/tex]
