Có bao nhiêu phát biểu sau là đúng (z, w là các số phức)

* Hướng dẫn giải

Đáp án B

$$\begin{gathered} \mathrm{Đặt} \mathrm{z}=\mathrm{a}+\mathrm{bi} \mathrm{và} \mathrm{w}=\mathrm{c}+\mathrm{di} (\mathrm{a};\mathrm{b};\mathrm{c};\mathrm{d}\in \mathrm{ℝ}) \\ \mathrm{z}=\overline{\mathrm{w}}\iff \left\{\begin{array}{l}\mathrm{a}=\mathrm{c}\\ \mathrm{b}=-\mathrm{d}\end{array}\iff {\mathrm{a}}^2+{\mathrm{b}}^2={\mathrm{c}}^2+{\mathrm{d}}^2\right. \\ \iff \sqrt{{\mathrm{a}}^2+{\mathrm{b}}^2}=\sqrt{{\mathrm{c}}^2+{\mathrm{d}}^2} \mathrm{hay} \left|\overline{\mathrm{z}}\right|=\left|\mathrm{w}\right| \\ \mathrm{z}=-\overline{\mathrm{w}} \iff \left\{\begin{array}{l}\mathrm{a}=-\mathrm{c}\\ \mathrm{b}=\mathrm{d}\end{array}\iff \right.\left\{\begin{array}{l}\mathrm{a}=-\mathrm{c}\\ -\mathrm{b}=-\mathrm{d}\end{array}\right.\mathrm{hay} \overline{\mathrm{z}}=-\mathrm{w} \\ \mathrm{Mặt} \mathrm{khác}: \mathrm{z}=\mathrm{w}\to {\mathrm{z}}^3={\mathrm{w}}^3 \\ \mathrm{KL}: \mathrm{Có} \mathrm{ý} 1; 2 \mathrm{và} 5 \mathrm{đúng} \end{gathered}$$