Answer
$(-4,-3)\cdot(6,-8)=-4(6)-3(-8)=0$
Work Step by Step
If the vectors are perpendicular, their dot product must be zero.
Dot product$=(-4,-3)\cdot(6,-8)=-4(6)-3(-8)=-24+24=0$.
Therefore, $-4\textbf {i}-3\textbf {j}$ and $6\textbf {i}-8\textbf {j}$ are perpendicular.