Recently I am having the online courses “Essential Mathematics for Computational Design” on https://www.rhino3d.education/ from Rajaa Issa. The course is great for me as I barely remember anything from high school mathematics…

Now I just get stuck on the lesson “vector dot product operation” (lesson4 of chapter2)
according to what I understand from the lesson, the dot product of two vectors should be always equal to the cosine of the vectors’ angle.

However, when I operated in the grasshopper, the result turns out differently.
Is there anything I did wrongly? Or did I not understand the concept? or is it a bug?