Chapter 12 - Vectors and the Geometry of Space - 12.5 Equations of Lines and Planes - 12.5 Exercises - Page 871: 14

No

Let $v_1$ be vector in the line containing the first two points. $v_1=\lt-1-(-2),1-4,1-0\gt$ $=\lt 3,-3,1\gt$ Let $v_2$ be vector in the line containing the second two points. $v_2=\lt3-2,-1-3,-8-4\gt$ $=\lt 1,-4,-12\gt$ Dot product of two vectors: $\lt 3,-3,1\gt$ \cdot $=\lt 1,-4,-12\gt$ $=3(1)+(-3)(-4)+1(-12)$ $=3$ They are not perpendicular.