Question Number 169900 by pticantor last updated on 12/May/22
$$\boldsymbol{{montrer}}\:\boldsymbol{{que}}\:\forall\boldsymbol{{z}}\in\mathbb{C}/\:\mid\boldsymbol{{z}}\mid=\mathrm{2}, \\ $$$$\mid\frac{\mathrm{1}}{\boldsymbol{{z}}^{\mathrm{4}} −\mathrm{5}\boldsymbol{{z}}+\mathrm{1}}\mid\leqslant\frac{\mathrm{1}}{\mathrm{5}} \\ $$