How do I find the sine of the angle between two vectors?
1 Answer
The sine of the angle between
(vec(u) xx vec(v))/(abs(u) abs(v))
Explanation:
I will assume you mean real valued two dimensional vectors..
Given vectors,
vec(u) = abs(u)((cos alpha) hat(i) + (sin alpha) hat(j))
vec(v) = abs(v)((cos beta) hat(i) + (sin beta) hat(j))
where
Then:
vec(u) xx vec(v) = abs(u) (cos alpha) abs(v) (sin beta) - abs(u) (sin alpha) abs(v) (cos beta)
color(white)(vec(u) xx vec(v)) = abs(u) abs(v) (cos alpha sin beta - sin alpha cos beta)
color(white)(vec(u) xx vec(v)) = abs(u) abs(v) sin (beta - alpha)
So:
sin (beta - alpha) = (vec(u) xx vec(v))/(abs(u) abs(v))
which is the sine of the angle between the two vectors.
Three dimensions
For
(abs(vec(u) xx vec(v)))/(abs(u) abs(v))