Question : Which of the following numbers is a divisor of $\left(49^{15}-1\right)$?
Option 1: 46
Option 2: 14
Option 3: 8
Option 4: 50
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Correct Answer: 8
Solution :
$\left(49^{15}-1\right)$
= $\left((7^2)^{15}-1\right)$
= $\left(7^{30}-1\right)$
We know that $a^n-b^n$ is divisible by $a+b$, when $a$ and $b$ are prime numbers, for any positive real number $n$.
So, $\left(7^{30}-1\right)$ is divisible by (7 + 1) = 8
Hence, the correct answer is 8.
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