Giải thích các bước giải:
a) $\sin\left(2x + \dfrac{\pi}{4}\right) = -1$
$\Leftrightarrow 2x + \dfrac{\pi}{4} = -\dfrac{\pi}{2} + k2\pi$
$\Leftrightarrow 2x = -\dfrac{3\pi}{4} + k2\pi$
$\Leftrightarrow x = -\dfrac{3\pi}{8} + k\pi\quad (k \in \Bbb Z)$
b) $\cos\left(\dfrac{x}{2} + \dfrac{\pi}{4}\right) = 0$
$\Leftrightarrow \dfrac{x}{2} + \dfrac{\pi}{4} = \dfrac{\pi}{2} + k\pi$
$\Leftrightarrow \dfrac{x}{2} = \dfrac{\pi}{4} + k\pi$
$\Leftrightarrow x = \dfrac{\pi}{2} + k2\pi \quad (k\in \Bbb Z)$
