Lời giải:\({\sin ^2}x + \sin x = 0 \Leftrightarrow \left[ \begin{array}{l}\sin x = 0\\\sin x = - 1\end{array} \right. \Leftrightarrow \left[ \begin{array}{l}x = k\pi \\x = - \frac{\pi }{2} + k2\pi \end{array} \right.\)
- \(x = k\pi \) vì \( - \frac{\pi }{2} < x < \frac{\pi }{2}\) nên :
\( - \frac{\pi }{2} < k\pi < \frac{\pi }{2} \Leftrightarrow - \frac{1}{2} < k < \frac{1}{2},k \in Z \Leftrightarrow k = 0 \Rightarrow x = 0\)
- \(x = - \frac{\pi }{2} + k2\pi \) vì \( - \frac{\pi }{2} < x < \frac{\pi }{2}\) nên :
\( - \frac{\pi }{2} < - \frac{\pi }{2} + k2\pi < \frac{\pi }{2} \Leftrightarrow 0 < k < \frac{1}{2},k \in Z \Leftrightarrow k \in \emptyset \)
