# Sinusoid format

I am having a bit of trouble understanding why, after we defined the sinusoid as (2.1), we changed the sin to a cos in (2.2).

Thanks.

• me too! In Fourier analysis we decompose signals into both sine and cosine components, or better stated individual complex frequencies $e^{j\omega t}$, since $e^{j\omega t}= cos(\omega t)+j sin(\omega t)$ – Dan Boschen May 11 '17 at 17:42