Angle Between 2 Lines

1. Angle \(\theta\) between 2 Lines having Direction Ratios Vectors (or Normal Vectors) \(\vec{A}\) and \(\vec{B}\) is given by the following formula
   
   \(\theta = \cos^{-1} (\frac{|\vec{A}\cdot\vec{B}|}{\vert \vec{A} \vert \vert \vec{B} \vert})\)
2. If \(\vec{A}\cdot\vec{B}=0\) then \(\theta=90^\circ\) and the Lines are Perpendicular to each other.
3. If \(\theta=0\) then the Lines are Parallel to or Co-Incident with each other.
4. In 2D and 3D only, if \(\vec{A}\times\vec{B}=0\) then the Lines are Parallel to or Co-Incident with each other.