# Quick dot product question

What is the dot product of a unit vector (e) with a non-unit vector (A)? Is this some sort of identity?

Thanks,
don_anon25

## Answers and Replies

don_anon25 said:
What is the dot product of a unit vector (e) with a non-unit vector (A)? Is this some sort of identity?

Thanks,
don_anon25

Let a be a unit vector and b be another vector. a * b = |a||b|cosθ. Since a is a unit vector, this becomes a * b = |b|cosθ. I believe that without more information, this is as far as it can be simplified.

robphy
Homework Helper
Gold Member
don_anon25 said:
What is the dot product of a unit vector (e) with a non-unit vector (A)? Is this some sort of identity?

Thanks,
don_anon25

$$\hat e\cdot\vec A$$ is the component of $$\vec A$$ along the $$\hat e$$-direction.