Explain the nature of Post-Traumatic Stress Disorder (PTSD).
Points:
(i) Meaning
(ii) Shock stage
(iii) Suggestible stage
(iv) Recovery stage
The slope of the tangent to the curve \( x = \sin\theta \) and \( y = \cos 2\theta \) at \( \theta = \frac{\pi}{6} \) is ___________.
Explain the construction of a spherical wavefront by using Huygens' principle.
The perpendicular distance of the plane \( r \cdot (3\hat{i} + 4\hat{j} + 12\hat{k}) = 78 \) from the origin is __________.