Answer
Not orthogonal vectors
Work Step by Step
If $ u \cdot v = 0 $ for two nonzero vectors $u=\left\langle a,b\right\rangle$ and $v=\left\langle c,d\right\rangle$, then $\cos \theta = 0 $ means $\theta= 90°$ and the vectors $u$ and $v$ are called orthogonal vectors.
The dot product is given by:
$u\cdot v=\left\langle a,b\right\rangle\cdot\left\langle c,d\right\rangle=ac+bd$
Now for $\left\langle 3,4\right\rangle$ and $\left\langle 6,8\right\rangle$ we have
$\left\langle 3,4\right\rangle\cdot\left\langle 6,8\right\rangle=(3)(6)+(4)(8)=18+32=50\neq0$.
Since $\left\langle 3,4\right\rangle\cdot\left\langle 6,8\right\rangle\neq0$, therefore the vectors $\left\langle 3,4\right\rangle$ and $\left\langle 6,8\right\rangle$ are not orthogonal vectors (to each other).
