(A) $L$.$H$.$S$. $= \frac{1+\sec \theta-\tan \theta}{1+\sec \theta+\tan \theta}$
$= \frac{1+\frac{1}{\cos \theta}-\frac{\sin \theta}{\cos \theta}}{1+\frac{1}{\cos \theta}+\frac{\sin \theta}{\cos \theta}}$ $\left[\because \sec \theta=\frac{1}{\cos \theta} \text{ and } \tan \theta=\frac{\sin \theta}{\cos \theta}\right]$
$= \frac{\cos \theta+1-\sin \theta}{\cos \theta+1+\sin \theta} = \frac{(\cos \theta+1)-\sin \theta}{(\cos \theta+1)+\sin \theta}$
Using the identity $1 = \sec^2 \theta - \tan^2 \theta$,we can write:
$= \frac{(\sec^2 \theta - \tan^2 \theta) + (\sec \theta - \tan \theta)}{1 + \sec \theta + \tan \theta}$
$= \frac{(\sec \theta - \tan \theta)(\sec \theta + \tan \theta) + (\sec \theta - \tan \theta)}{1 + \sec \theta + \tan \theta}$
$= \frac{(\sec \theta - \tan \theta)(\sec \theta + \tan \theta + 1)}{1 + \sec \theta + \tan \theta}$
$= \sec \theta - \tan \theta$
$= \frac{1}{\cos \theta} - \frac{\sin \theta}{\cos \theta} = \frac{1-\sin \theta}{\cos \theta} = \text{R.H.S.}$
Hence proved.