In thermodynamics, the surroundings encompass everything outside the system being studied. This includes all external objects and the environment that can exchange energy and matter with the system.
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 ___________.