Explanation: \(\text{Hints: } \sin A = \cos\left(\frac{\pi}{2} \pm A\right)\) \(\text{Solve: } x_1 = A \sin \omega t\) \[ x_2 = A \cos \omega t = A \sin\left(\frac{\pi}{2} + \omega t\right) \] \[ \therefore \text{দফা পার্থক্য } = \left(\frac{\pi}{2} + \omega t\right) - \omega t = \frac{\pi}{2} \] \(\text{Ans. (D)}\) \(\text{ব্যাখ্যা: } x = A \sin \omega t \text{ এবং } x = A \cos \omega t \text{ এর গ্রাফ।}\)