Imagine a unit circle (radius 1, centred on the origin 0,0). Starting from the positive x-axis (or 'east' direction) go anticlockwise however many degrees you want to. If it's negative angle then go clockwise. The sin axis is the y axis and the cos axis is the x axis. So sin(-180) would therefore be 0. It's also useful to just memorise the shapes of the graphs of sin and cos as they are very common functions throughout a level.