(2)To anticipate a question which may appear later, the fact that modulation “makes negative frequencies appear in the positive spectrum” is really a consequence of the following very mundane formula:
![cosα cosβ = 1[cos(α +β) +cos(α - β)]
2](livre241x.png)
(2)To anticipate a question which may appear later, the fact that modulation “makes negative frequencies appear in the positive spectrum” is really a consequence of the following very mundane formula: