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# C4 Vectors scalar product

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1. Hi so I understand the dot product of two vectors and how to manipulate it to find the angle between them

i dont however understand how the two vectors must be oriented; if there is a triangle ABC, to find the angle ABC, do you dot product B->A with B->C or ??

i have also added a picture illustrating my confusion, hope the quality isnt too bad

any help is much appreciated, thanks
2. (Original post by hi-zen-berg)
Hi so I understand the dot product of two vectors and how to manipulate it to find the angle between them

i dont however understand how the two vectors must be oriented; if there is a triangle ABC, to find the angle ABC, do you dot product B->A with B->C or ??

i have also added a picture illustrating my confusion, hope the quality isnt too bad

any help is much appreciated, thanks
If you're interested in the angle at B, then you want both vectors coming out from B, i.e. BA.BC. That's the easiest method to remember. Imagine you're sitting at B, looking out, one vector is BA, the other BC.

It also works if both vectors are going in to B, i.e. AB.CB

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