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Why is the calculated angle between two vectors always between $\pi$ and $0$.

Is this due to the limitations of $\arccos\theta$ or is it because angles between vectors is described to be the smaller one?

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It's a matter of tradition and simplicity.

Each pair of vectors defines two angles. One of them is between $0$ and $\pi$ and the other is between $\pi$ and $2\pi$. Since their sum is $2\pi$, we only really need to tell one of the two angles, and we decide, for simplicity, to always report the smaller of the two.

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    $\begingroup$ It might be worth additionally pointing out that in certain (?) settings, like the plane, we can make a canonical choice of the "direction of the angle", and thus report the angle from a vector to another to always be the one in positive (counter-clockwise) direction. In more general settings such a canonical direction is not available. $\endgroup$ – Mees de Vries Apr 23 at 11:49
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There are angles of all possible degrees. In context with angles in a triangle however, we have $0\le \theta \le \pi$.

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