2nπ2 n \pi2nπ
(2n+1)π(2 n+1) \pi(2n+1)π
(2n+1)π2(2 n+1) \frac{\pi}{2}(2n+1)2π
(2n+1)π4(2 n+1) \frac{\pi}{4}(2n+1)4π