اتحادهای مثلثاتی زیر را ثابت کنید: الف) $\frac{1}{1-\sin\theta} + \frac{1}{1+\sin\theta} = \frac{2}{\cos^{2}\theta}$ ج) $\frac{1}{\cos\theta} - \cos\theta = \tan\theta\sin\theta$ هـ) $\frac{1}{\sin^{2}\theta} + \frac{1}{\tan^{2}\theta} = \frac{1}{\sin^{2}\theta\tan^{2}\theta}$ و) $\cos^{2}\theta - \sin^{2}\theta = 1 - 2\sin^{2}\theta$ ط) $(2\sin^{2}\theta - 1)(1 - 2\sin^{2}\theta) = \sin^{4}\theta - \cos^{4}\theta$ ک) $\frac{2\tan\theta}{1+\tan^{2}\theta} = 2\sin\theta\cos\theta$ م) $\cos^{2}\theta(2 + \tan^{2}\theta) = 2 - \sin^{2}\theta$