How to flip a Quaternion to face the opposite direction, without knowing the axis

Hello there. My question is probably more complicated than it seems (or perhaps it’s a lot more simple - I don’t know…).

I’ve checked various questions, documentation and posts here, but I remain unclear about this…

I’d like to know if Quaternion.Inverse ‘flips’ the rotation around 180 degrees, or does it return a rotation that would, when multiplied (added, I guess) to the original, produce an identity Quaternion? That is, one without any rotation.

To me, it seems like the ‘inverse’ of a rotation is different to a rotation facing in the opposite direction. The opposite direction, when multiplied (added) to the original will not send the rotation back to ‘0’, right? It will make it U-turn.

So how do I ‘flip’ a Quaternion 180 degrees, without necessarily knowing the axis?
Cheers.

Try

Quaternion rot180degrees = Quaternion.Euler(-originalRot.eulerAngles)

You are correct, Inverse returns the multiplicative inverse of the Quaternion.

print(Quaternion.Inverse(quat) * quat == Quaternion.identity); // Prints true
print(Quaternion.Euler(-quat.eulerAngles) * quat == Quaternion.identity); // Prints false