Q21. Three vectors $\overrightarrow { \mathrm { OP } } , \overrightarrow { \mathrm { OQ } }$ and $\overrightarrow { \mathrm { OR } }$ each of magnitude A are acting as shown in figure. The resultant of the three\\
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vectors is $\mathrm { A } \sqrt { x }$. The value of $x$ is $\_\_\_\_$。