$\overrightarrow{P},\overrightarrow{Q},\overrightarrow{R},\overrightarrow{S}$ are vector of equal magnitude. If  $\overrightarrow{P} + \overrightarrow{Q} - \overrightarrow{R} = 0$ angle between  $\overrightarrow{P}$ and  $\overrightarrow{Q}$ is   ${\theta }_1$ . If  $\overrightarrow{P} + \overrightarrow{Q} - \overrightarrow{S} = 0$ angle between  $\overrightarrow{P}$ and  $\overrightarrow{S}$ is ${\theta }_2$. The ratio of ${\theta }_1$ to ${\theta }_2$ is