To express \( 3^{-1/2} \) using the negative exponent rule, we can rewrite it as:
\[ 3^{-1/2} = \frac{1}{3^{1/2}} \]
Next, to express \( 3^{1/2} \) in radical form, we have:
\[ 3^{1/2} = \sqrt{3} \]
So, putting it all together, we can write:
\[ 3^{-1/2} = \frac{1}{\sqrt{3}} \]
Thus, the equivalent expression of \( 3^{-1/2} \) in radical form is:
\[ \frac{1}{\sqrt{3}} \]