\[\boxed{\mathbf{498}.}\]
\[1)\ 7^{x\sqrt{3}} = \sqrt{7};\]
\[7^{x\sqrt{3}} = 7^{\frac{1}{2}};\]
\[x\sqrt{3} = \frac{1}{2};\]
\[x = \frac{1}{2\sqrt{3}} = \frac{\sqrt{3}}{2 \bullet 3} = \frac{\sqrt{3}}{6};\]
\[Ответ:\ \ x = \frac{\sqrt{3}}{6}.\]
\[2)\ 25^{x\sqrt{2}} = 5\sqrt{5};\]
\[\left( 5^{2} \right)^{x\sqrt{2}} = 5^{1} \bullet 5^{\frac{1}{2}};\]
\[5^{2x\sqrt{2}} = 5^{1 + \frac{1}{2}};\]
\[2x\sqrt{2} = \frac{3}{2};\]
\[x = \frac{3}{2 \bullet 2\sqrt{2}} = \frac{3\sqrt{2}}{2 \bullet 2 \bullet 2} = \frac{3\sqrt{2}}{8};\]
\[Ответ:\ \ x = \frac{3\sqrt{2}}{8}.\]
\[3)\ \left( \sqrt{3} \right)^{3x} = 3\sqrt{3};\]
\[\left( 3^{\frac{1}{2}} \right)^{3x} = 3^{1} \bullet 3^{\frac{1}{2}};\]
\[3^{\frac{3x}{2}} = 3^{1 + \frac{1}{2}};\]
\[\frac{3x}{2} = \frac{3}{2}\]
\[\ x = \frac{3}{2} \bullet \frac{2}{3} = 1;\]
\[Ответ:\ \ x = 1.\]