Transplanting:
- Transplanting is carried out in well-prepared fields once the seedlings reach a height of 10-15 cm.
- Spacing of 75 cm between rows and 50 cm between plants is ideal for proper aeration and growth.
- Transplanting should be done in moist soil, preferably after light irrigation or rainfall.
- For the initial few days, shading is provided to minimize transplant shock.
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 ___________.