Solution

ID: past-exam-of-the-mathematics-course-of-the-year-1-of-the-natural-sciences-course-of-the-university-of-cambridge/2024/paper-2/20/a/solution

The wave equation is a homogeneous linear partial differential equation. Consequently, if and solve it, every constant linear combination also solves it. This is the superposition principle, because partial differentiation distributes over the linear combination.
The same statement holds for the homogeneous Neumann boundary conditions. Initial conditions combine in the same way; an arbitrary combination need not retain a fixed nonzero initial displacement.

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