If you're going for simple motion there is an easy shortcut you can take. If you're doing something like Pong or breakout all you need to do is reverse the delta of horizontal or vertical component.
So if the ball hits the top make the ball start to move down, if it hits the left make it move right. No need to calculate any angles.
I only say this because years ago I was making a pong type game with complex angle calculations, when someone pointed out that all I needed to do is the above :oops:
