De Broglie Matter Waves: Where Does the Fraction Come From?

[Matter_Matters]

In de Broglie's original proof of the theorem of phase harmony, the frequency of the moving wave of energy mc^2 (not the internal periodic phenomenon wave) is multiplied by the following term

$freq * ( t - \frac{\beta * x}{c} )$

Does anyone have an idea where the fraction comes from? All help appreciated.

 

[Matter_Matters]

Never mind... I got it! answer is on pg 40 of de Broglie's introduction to wave mechanics!