Question

The vectors (-4, -8) and (2, k) are perpendicular. Find k.k=Ü:Х?

Answer 1

`k=-2`

Explanation:

We have two vectors, both of which are perpendicular:

If the vectors are perpendicular, then θ = π/2

Hence,

`\begin{gathered} u\cdot v=\lvert u\rvert\lvert v\rvert\cos ((\pi)/(2)) \\ u\cdot v=0 \\ \text{Therefore,} \\ 0=(-4\cdot2)+(-8\cdot k) \\ 8k=-16 \\ k=-(16)/(8) \\ k=-2 \end{gathered}`