There's a section in Gibson's "Elementary Geometry of Differentiable Curves:An Undergraduate Introduction" book on page 6:
"Example 1.4: Recall that the component of a vector in the direction of a unit vector is the vector . (Example 1.1)
It is useful to express this in complex notation. Note that for any vectors we have : in particular when
b is a unit vector (i.e. ) we have ."
What I don't understand is why and how is: ?
The author said(given above) and I quote "for any vectors" this is true.
Can anyone kindly shed light on this and explain a bit why this is so?