求助！

lawrence425

1. Given the relation:
ω=α^2 β^1/3
ω is angular frequency and β is propagation constant.
(a) Calculate the phase velocity.
(b) Calculate the group velocity.
(c) Derive an expression for dispersion parameter D.
Note: is a constant.

谢谢！

shaka2007

传播常数和角频率给了，求相速度和群速度，好像有公式吧，记不清了