Prove the identities

1. $${\tan }^{2}x+1=\frac{1}{{\cos }^{2}x}$$
2. $$\frac{{\tan }^2\theta -1}{\sin \theta +\cos \theta }=\frac{\tan \theta -1}{\cos \theta }$$
3. $$\frac{\cos \phi +\sin \phi }{1-{\tan }^2\phi }=\frac{{\cos }^2\phi }{\cos \phi -\sin \phi }$$