So while deriving equation for the velocity of particle executing SHM at any point, I noticed a difference in the result depending on what wave (sine or cosine) you chose.

> 
> For $x=A\cos\omega t$:  
> 
> $\quad \ \,v=-\omega\sqrt{A^2-x^2}$  
> 
> For $x=A\sin\omega t$:  
> 
> $\quad \ \,v=\omega\sqrt{A^2-x^2}$
> 
> 
> 

Can anyone explain to me why the difference is there and what it means, since both equation are basically the same with only a phase difference?