[MerryDeer]

Hi,

I'am making pool. I have ball, with angle, how to get oposite angle? if i add just -angle, it's not always correct, maybe there is another way?

[NaS]

A negative angle does not "revert" the direction, that in fact only works for 90°. This operation changes a clockwise angle to counter-clockwise, which is something different.

You can add or substract 180.0 to/from the angle to make it face the opposite direction.