Mathematics

Problem

Two unit vectors

\vec{p}

and

\vec{q}

satisfy

\vec{p}\,\cdot\,\vec{q}<0

. Which statement about the angles

\theta_p

and

\theta_q

they make with the positive

x

–axis is necessarily true? a)

|\theta_p+\theta_q|=180^{\circ}

|\theta_p-\theta_q|<90^{\circ}

|\theta_p-\theta_q|>90^{\circ}

|\theta_p-\theta_q|=90^{\circ}