If x > 0, and $x^4 +\frac{1}{x^4} =2207$, what is the value of $x^7 +\frac{1}{x^7}$?

710647

If x > 0, and $x^4 +\frac{1}{x^4} =2207$

$x^7 +\frac{1}{x^7}$ = ?

In this type of questions the unit digit of  $x^4 +\frac{1}{x^4}$ is always same as the unit digit of $x^7 +\frac{1}{x^7}$

So going through the options then we have 710647 option that has the unit digit same with the given question.