$ \sigma = E \epsilon $

sigma = E * epsilon

$ c ^2 = \displaystyle\frac{ E }{ \rho }$

c ^2 = E / rho

$\displaystyle\frac{\partial^2 u}{\partial t^2}= c ^2\displaystyle\frac{\partial^2 u}{\partial x^2}$

@DIF( u , t , 2) = c ^2*@DIF( u , x , 2)

$ z = z_0 e^{ i( k s - \omega t )}$

z = z_0 * exp( %i *( k * s - omega * t ))

$ i k z = 0$

%i * k * z = 0

$ z = 0$

z = 0

$ \lambda_s = \displaystyle\frac{2 L }{ n_s }$

lambda_s = 2* L / n_s

$ \lambda_a = \displaystyle\frac{4 L }{2 n_a + 1}$

lambda_a = 4 * L /(2* n_a + 1)

$ \nu_s = \displaystyle\frac{ n_s }{2 L } c $

nu_s = n_s * c /(2* L )

$ \nu_a = \displaystyle\frac{2 n_a + 1}{4 L } c $

nu_a = (2* n_a + 1) * c /(4 * L )