Chapter 12 - Vectors and the Geometry of Space - 12.5 Equations of Lines and Planes - 12.5 Exercises - Page 872: 55

parallel

$n_1=\lt2,-3,-1\gt$ and $n_2=\lt -4,6,2\gt$ Angle between two vectors$\theta= cos^{-1}|\dfrac{a.b}{|a||b|}|$ $\theta= cos^{-1}|\dfrac{-1}{\sqrt {11} \sqrt {11}}|$ $\theta= cos^{-1}|\dfrac{-28}{\sqrt {14}\sqrt {56}}|$ $=cos^{-1}[-1]$ $=180 ^{\circ}$ Hence, the two planes are parallel.