Trignometry

\frac{\sin \theta+\alpha}{\cos \theta-\alpha}=\frac{\sin\theta\cos\alpha+\cos\theta\sin\alpha}{cos\theta\cos\alpha +\sin\theta\sin\alpha}

.\qquad \qquad=\frac{\tan\theta+\tan\alpha}{1+\tan\theta\tan\alpha}=\frac{1-m}{1+m}

m=\frac{1+\tan\theta\tan\alpha-\tan\theta-\tan\alpha}{1+\tan\theta\tan\alpha+\tan\alpha+\tan\alpha}

.\qquad\qquad=\frac{(1-\tan\theta)(1-\tan\alpha)}{(1+\tan\theta)(1+\tan\theta)}=\tan(\pi/4-\theta)\tan(\pi/4-\alpha)