- HD 2967: A high-yielding variety, popular in North India.
- PBW 343: Ideal for late-sown conditions.
- WH 1105: Known for its disease resistance.
- Lok-1: Commonly cultivated in Central and Western India.
Explain the construction of a spherical wavefront by using Huygens' principle.
The slope of the tangent to the curve \( x = \sin\theta \) and \( y = \cos 2\theta \) at \( \theta = \frac{\pi}{6} \) is ___________.