প্রদত্ত সমীকরণ, $$ \begin{aligned} \sin 3x &= \cos x \\ \Rightarrow \cos\left(\frac{\pi}{2} - 3x\right) &= \cos x \\ \Rightarrow \frac{\pi}{2} - 3x &= 2n\pi \pm x \end{aligned} $$ ধনাত্মক চিহ্ন নিয়ে, $$ \begin{aligned} \frac{\pi}{2} - 3x &= 2n\pi + x \\ \Rightarrow 4x &= \frac{\pi}{2} - 2n\pi \\ \Rightarrow x &= \frac{\pi}{8} - \frac{n\pi}{2} \end{aligned} $$ $n=0$ হলে, $x = \frac{\pi}{8} = 22.5^{\circ}$। ঋণাত্মক চিহ্ন নিয়ে, $$ \begin{aligned} \frac{\pi}{2} - 3x &= 2n\pi - x \\ \Rightarrow 2x &= \frac{\pi}{2} - 2n\pi \\ \Rightarrow x &= \frac{\pi}{4} - n\pi \end{aligned} $$ $n=0$ হলে, $x = \frac{\pi}{4} = 45^{\circ}$। সুতরাং, সমাধান $22.5^{\circ}, 45^{\circ}$। সঠিক উত্তর: D