Answer:
n=2
Step-by-step explanation:
Hello, please consider the following.
[tex]{5}^{n + 1} - {5}^{n} + {5}^{n - 1} = 105\\\\5^{n-1}(5^2-5+1)=5^{n-1}(25-5+1)=21*5^{n-1}=105\\\\5^{n-1}=\dfrac{105}{21}=5=5^1\\\\\text{It means that}\\\\n-1=1 <=> n=2[/tex]
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Thank you
