Hi,

I have kind of a meta question about **trigonometry**!

Am I right in assuming that the following calculation/formula gives me the angle *alpha* between a two-dimensional vector and the x-axis of a plane (i.e. xy-plane)?

For the **y-coordinate** of the vector being **bigger than 0**:

- alpha = acos(vector x / vector length)

For the **y-coordinate** being **smaller or equal to 0**:

- alpha = 2 x Pi - acos(vector x / vector length)

Furthermore, how would I go about introducing 3D space into this? I mean calculating the angle for three-dimensional vectors? This would only be possible in the local plane of the vector and the x-axis, wouldn’t it?

As always, thanks.