Velocity of Wave Packets

Hyperreality

Wave packets has a group velocity of

[tex]v_{group}=\frac{d\omega}{dk}[/tex]

and its phase velocity is

[tex]v_{phase}=\frac{\omega}{k}[/tex]

Show that the group velocity and the phase velocity are related by:

[tex]v_{group} = v_{phase} - \lambda\frac{dv_{phase}}{d\lambda}[/tex]

Can someone please tell me where to start on this problem?

dextercioby

All u need to know besides the rules of differentiation is
[tex] k=:\frac{2\pi}{\lambda} [/tex]

Daniel.

PS.Compute the RHS of your equality and show it matches the LHS.