\( \frac{1 + \sin \theta}{1 - \sin \theta} - \frac{1 - \sin \theta}{1 + \sin \theta} = \frac{1 + 2 \sin \theta + \sin^{2} \theta - (1 - 2 \sin \theta + \sin^{2} \theta)}{1 - \sin^{2} \theta} = \frac{4 \sin \theta}{1 - \sin^{2} \theta} = \frac{4 \sin \theta}{\cos^{2} \theta} \) عبارت نهایی در کادر: \( \frac{4 \sin \theta}{\cos^{2} \theta} = 4 \tan \theta \)