What happens if **cos( )** is replaced with **sin( )**?
Consider the following equation:

When **cos( )** is replaced with **sin( )**, the graph is
rotated /2*k*
radians, as in the following examples.

Conclusions: Replacing cosine with sine

When **cos( )** is replaced with **sin( )** in the
equation

we have

The graph is rotated /2*k*
radians.