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How do you prove :

$ \forall n \in \mathbb{N}$ if $ u_n=\Re(({\frac{1+i\sqrt{7}}{2}})^n) $ where $\Re$ mean the real part of a complex number, that $$ \lim_{n\rightarrow +\infty}\left | u_n \right |=+\infty$$

$\left | u_n \right |$ is the modulus of $u_n$

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