Question

How to determine if vectors are parallel?

Answer 1

One could use the relation


`\mathbf a\cdot\mathbf b=\|\mathbf a\|\|\mathbf b\|\cos\theta`

where
`\mathbf a,\mathbf b` are two vectors,
`\|\mathbf a\|` denotes the norm of that vector, and
`\theta` is the angle between the two vectors.

Then the two vectors will be parallel if
`\theta=0` or
`\pi`.