USAMO GuideUSAMOGuide
Back to Problems
PrevNext
1200
Cosine Sum
Editorial
trigonometryroots of unitysequencesperiodicity
Evaluate the sum:
∑n=12025cos⁡ ⁣(nπ4).\sum_{n=1}^{2025} \cos\!\left(\frac{n\pi}{4}\right).
Round your answer to three decimal places.

Sign in to submit your answer