Derive v = 2 l_nf_n for the nth harmonic

[Northbysouth]

Homework Statement

Derive the expression v = l_nf_n where l_n is the shortest distance between nodes for the n^th harmonic.

Homework Equations

v = wave speed
l_n = shortest distance between nodes for the n^thharmonic
f_n = frequency of the n^th harmonic

The Attempt at a Solution

Is it asking me to take the derivative of the wave speed, which I believe would give me the acceleration of the wave?

So,

wave acceleration = 2*l_n

Am I making any sense?

 

[rl.bhat]

nth harmonics of fo is n times fo. Similarly ln is equal to (lambda)o/2n.
Now proceed.