Bonsoir,
Il faut utiliser la propriété: [tex]\dfrac{1}{a+ib} = \dfrac{a-ib}{a^2+b^2}[/tex]
a)
[tex]\dfrac{1}{1+4i} = \dfrac{1 - 4i}{1^2+4^2}=\dfrac{1-4i}{17} = \dfrac{1}{17}-\dfrac{4i}{17}\\\\[/tex]
b)
[tex]\dfrac{1}{-3-5i} = \dfrac{-3-5i}{(-3)^2+(-5)^2}=\dfrac{-3-5i}{34} = -\dfrac{3}{34}+\dfrac{5i}{34}\\\\[/tex]
