Mathematics

Problem

Two vectors

\mathbf{u}

and

\mathbf{v}

satisfy

\mathbf{u}\cdot\mathbf{v}=-15

|\mathbf{u}|=5

and

|\mathbf{v}|=6

. Determine whether the angle between

\mathbf{u}

and

\mathbf{v}

is acute, right, or obtuse, giving a brief reason.