Kí hiệu \({z_1},{z_2}\) là hai nghiệm phức của phương trình \({{\rm{z}}^2} + z + {2019^{2018}} = 0.\) Giá trị \(\left| {{z_1}} \right| + \left| {{z_2}} \right|\) bằng

* Hướng dẫn giải

Ta có \({{\rm{z}}^2} + z + {2019^{2018}} = 0 \Leftrightarrow {\left( {z + \dfrac{1}{2}} \right)^2} - \dfrac{1}{4} + {2019^{2018}} = 0 \Leftrightarrow {\left( {z + \dfrac{1}{2}} \right)^2} = \dfrac{1}{4} - {2019^{2018}}\)

\( \Leftrightarrow {\left( {z + \dfrac{1}{2}} \right)^2} = \left( {{{2019}^{2018}} - \dfrac{1}{4}} \right).{i^2} \Leftrightarrow \left[ \begin{array}{l}z =  - \dfrac{1}{4} - \sqrt {{{2019}^{2018}} - \dfrac{1}{4}} .i\\z =  - \dfrac{1}{4} + \sqrt {{{2019}^{2018}} - \dfrac{1}{4}} .i\end{array} \right.\)

Suy ra \({z_1} =  - \dfrac{1}{2} - \sqrt {{{2019}^{2018}} - \dfrac{1}{4}} .i \Rightarrow \left| {{z_1}} \right| = \sqrt {{{\left( { - \dfrac{1}{2}} \right)}^2} + {{2019}^{2018}} - \dfrac{1}{4}}  = \sqrt {{{2019}^{2018}}}  = {2019^{1009}}\)

\({z_2} =  - \dfrac{1}{2} + \sqrt {{{2019}^{2018}} - \dfrac{1}{4}} .i \Rightarrow \left| {{z_2}} \right| = \sqrt {{{\left( { - \dfrac{1}{2}} \right)}^2} + {{2019}^{2018}} - \dfrac{1}{4}}  = \sqrt {{{2019}^{2018}}}  = {2019^{1009}}\)

Do đó \(\left| {{z_1}} \right| + \left| {{z_2}} \right| = {2019^{1009}} + {2019^{1009}} = {2.2019^{1009}}\)

Chọn D.