\[b > 5:\]
\[(b - 5)\sqrt{\frac{3}{b^{2} - 10b + 25}} =\]
\[= (b - 5)\sqrt{\frac{3}{(b - 5)^{2}}} =\]
\[= \frac{b - 5}{b - 5}\sqrt{3} = \sqrt{3}.\]