# Trouble understanding aspect of SHM

## Homework Statement

When deriving the basic equations for SHM, you get the
$$a_c = /omega^2 A$$
and then continue on to derive
$$a_x = -a_c cos/theta$$
I was wondering where the negative sign came from in the equation above. I don't see the need for it, the x component of the centripetal acceleration seems to point in the same direction as the acceleration "projected onto a diameter" already.

ps why aren't my latex commands for omega and theta not working?