MathCastle
TrigonometrySuperchallengeInverse Trigonometric Functions

Inverse Trigonometric Functions · Superchallenge problem

Using the identity arctan⁡12k2=arctan⁡12k−1−arctan⁡12k+1\arctan\dfrac{1}{2k^{2}}=\arctan\dfrac{1}{2k-1}-\arctan\dfrac{1}{2k+1}, evaluate the infinite telescoping sum

arctan⁡12+arctan⁡18+arctan⁡118+arctan⁡132+⋯=∑k=1∞arctan⁡12k2.\arctan\dfrac12+\arctan\dfrac18+\arctan\dfrac{1}{18}+\arctan\dfrac{1}{32}+\cdots=\sum_{k=1}^{\infty}\arctan\dfrac{1}{2k^{2}}.