Mathematics

Problem

The non-zero vectors

\mathbf{a}

\mathbf{b}

and

\mathbf{c}

are related by

\mathbf{a} = 8\mathbf{b}

and

\mathbf{c} = -7\mathbf{b}

. Then, the angle between

\mathbf{a}

and

\mathbf{c}

is a.

\pi

0

\frac{\pi}{4}

\frac{\pi}{2}