 Solution

ID: past-exam-of-the-mathematics-course-of-the-year-1-of-the-natural-sciences-course-of-the-university-of-cambridge/2016/paper-2/7/b/solution

Differentiation of the finite sum involves no convergence issue. The derivative has the Fourier cosine series

f^{'} (x) = cos x + 2 cos 2 x + 3 cos 3 x .

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