Chapter 9 - Section 9.2 - The Dot Product - 9.2 Exercises - Page 646: 16

These two vectors are perpendicular

$\vec{u}=\langle0,-5\rangle$ $,$ $\vec{v}=\langle4,0\rangle$ Find $\vec{u}\cdot\vec{v}$ by multiplying corresponding components and adding: $\vec{u}\cdot\vec{v}=(0)(4)+(-5)(0)=0+0=0$ Since the dot product of these two vectors is equal to $0$, these two vectors are perpendicular.