What is the origin of the minus sign in the derivatives of an oscillating body?

[Ugnius]

Homework Statement

Body of mass 0.2kg is oscillating. A = 5cm , w=π rad/s , t = 1/6 s. Find the force and momentum.

Relevant Equations

s(t) = Asin(wt)

I know it is a quite simple task.
p = mv and F=ma.
All i need to do is find the normal and double derivatives of s(t). But here's the problem , i have the answers and they state that first derivative is v =
-Awcoswt and second is -Aw^2sinwt. Everything is quite clear to me, but I am wondering can someone explain where the minus before A comes from?

 

[etotheipi]

It's a mistake, $\frac{ds(t)}{dt} = A\omega \cos{\omega t}$, whilst $\frac{d^2s(t)}{dt^2} = -A\omega^2 \sin{\omega t}$.