Sajad

4 / √84  =

4 / √ [ 4 * 21 ]   =

4 /  [ 2 √21  ]   =

2 / √21

$\frac{4}{\sqrt{84}}$

$\frac{4}{\sqrt{4\times21}}$

$\frac{4}{\sqrt{4}\sqrt{21}}$

$\frac{4}{2\sqrt{21}}$

$\frac{4}{2\sqrt{21}}\frac{\times}{\times}\frac{\sqrt{21}}{\sqrt{21}}$

$\frac{4\sqrt{21}}{2\times21}$

$\frac{4\sqrt{21}}{42}\frac{÷}{÷}\frac{2}{2}$

$\frac{2\sqrt{21}}{21}$

$\frac{2\times 4.58257569495584...}{21}$

$\frac{9.16515138991168...}{21}$

$0.43643578047198476...$