The non-zero vectors $\vec b$ and $\vec c$ are related by $\vec a=8\vec b$ and $\vec c =-7\vec b$. Then the angle between $\vec a$ and $\vec c$, is
Answer & explanation
Correct answer: option 4
We have, $\vec a =8b$ and $\vec c =-7b$
$⇒\vec a=\frac{-8}{7}\vec c$
$⇒\vec a$ and $\vec c$ are unlike parallel vectors.
⇒ Angle between $\vec a$ and $\vec c$ is $π$.