2πn2 \pi \mathrm{n}2πn
2n(λ2)2 \mathrm{n}\left(\frac{\lambda}{2}\right)2n(2λ)
(2n+1)π(2 n+1) \pi(2n+1)π
(n+12)λ\left(n+\frac{1}{2}\right) \lambda(n+21)λ