Who is known as the father of Indian Bryology?

In a triangle $ABC$,with usual notations,if $\frac{2 \cos A}{a} + \frac{\cos B}{b} + \frac{2 \cos C}{c} = \frac{a}{bc} + \frac{b}{ca}$,then $\angle A = $

Electron affinity is the

$\int_0^{\pi/6} \cos^4 3\theta \cdot \sin^2 6\theta \, d\theta$ is equal to

An azeotropic solution of two liquids has a boiling point lower than either of them when it:

In the half-wave rectifier circuit shown,which one of the following waveforms is true for $V_{CD}$,the output across $C$ and $D$?