It's the triangle 30° - 60° - 90°.
The sides are in proportion 1 : √3 : 2 (look at the picture).
Therefore we have:
[tex]x=\dfrac{\sqrt6\cdot\sqrt3}{2}=\dfrac{\sqrt{(6)(3)}}{2}=\dfrac{\sqrt{18}}{2}=\dfrac{\sqrt{(9)(2)}}{2}\\\\=\dfrac{\sqrt9\cdot\sqrt2}{2}=\boxed{\dfrac{3\sqrt2}{2}}[/tex]
