Question:
If $\overrightarrow{\mathrm{P}} \times \overrightarrow{\mathrm{Q}}=\overrightarrow{\mathrm{Q}} \times \overrightarrow{\mathrm{P}}$, the angle between $\overrightarrow{\mathrm{P}}$ and $\overrightarrow{\mathrm{Q}}$ is $\theta\left(0^{\circ}<\theta<360^{\circ}\right)$. The value of ' $\theta^{\prime}$ will be_______ $\circ$.
Solution:
$-P Q \sin \theta$
$=P Q \sin \theta$
$\Rightarrow \theta=180^{\circ}$