The sin and cos in my example was actually from another program which I manipulated to work in my program although I didn't understand the maths behind it at the time. I've done a bit more playing around and basically, you can used the concept of projectile motion without gravity to move your sprite at a chosen angle.
In a nutshell:
x velocity = Vcos(angle) where v is your initial velocity (desired speed) and the angle is the direction you want your sprite to move in.
y velocity = Vsin(angle) same as above.
Attached an example of the above. Hope the comments make sense
If you want more info, google "Projectile Motion" and "Unit Circle"
A clever person solves a problem, a wise person avoids it - Albert Einstein
