(c)
On comparing the given equation with standard equation, we get
$a = \cos\theta - \sin\theta,\ b = \cos\theta + \sin\theta,\ h = \cos\theta$
$\tan\phi = \frac{2\sqrt{\cos^{2}\theta - \left( \cos^{2}\theta - \sin^{2}\theta \right)}}{\cos{\theta - \sin{\theta + \cos{\theta +}\sin\theta}}} = \frac{2\sin\theta}{2\cos\theta}$
$\Rightarrow \tan\phi = \tan\theta \Rightarrow \phi = \theta$