How can I plot the angle value between two 3D vectors

Questions
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1

I have two vectors, v1 and v2. I can plot them and calculate the angle between them without any problem. I would like to plot this angle (theta) between them on my plot.

I know that I could draw an arc between the two vectors with a small radius to show an angle measurement, but I am unsure how I can navigate the new plane defined by the two vectors.

Any suggestions as to how I could do this? My work is attached.

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2

Here’s one way to draw an arrow from v1 to v2:

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3

Thank you, Michael. This is EXACTLTY what I need. I was not familiar with the Orthogonalize function, but I understand what you have done here. Thank you.

4

This adds a circular sector:

radius = .2;
arc = Table[
   origin + radius*Normalize[t v1 + (1 - t) v2 - origin], {t, 0, 1, 
    1/10}];
Graphics3D[{Red, Arrow[{origin, v1}], Black, Arrow[{origin, v2}],
  Arrow[Reverse@arc], Opacity[.3], Polygon[Append[arc, origin]]},
 Axes -> True, Boxed -> True]
5

Thank you, Gianluca. This is helpful.