6.1. Fundamental properties of bounded linear operators between normed vector spaces6.2. The operator norm, convergence of operator sequences and Banach algebras6.3. Invertibility of linear operators6.4. The dual of a Hilbert space and the Riesz representation theorem6.5. Bilinear forms, sesquilinear forms and associated quadratic forms6.6. The adjoint operator: presentation and properties6.7. Orthogonal projection operators in a Hilbert space6.8. Isometric and unitary operators6.9. The Fourier transform on S(ℝn), L1(ℝn) and L2(ℝn)6.10. The Nyquist-Shannon sampling theorem6.11. Application of the Fourier transform to solve ordinary and partial differential equations6.12. Summary