8. \( \left(\frac{36}{64}\right)^{-\frac{3}{2}} \quad \) 9. \( (2,25)^{-\frac{1}{2}} \)

To solve \( \left(\frac{36}{64}\right)^{-\frac{3}{2}} \), we first simplify the fraction. The fraction can be reduced to \( \left(\frac{9}{16}\right)^{-\frac{3}{2}} \). Using the property of negative exponents, this becomes \( \left(\frac{16}{9}\right)^{\frac{3}{2}} \). Calculating \( \frac{16}{9} \) to the power of \( \frac{3}{2} \) means we first take the square root, giving us \( \frac{4}{3} \), then raise it to the third power: \( \left(\frac{4}{3}\right)^3 = \frac{64}{27} \). For \( (2.25)^{-\frac{1}{2}} \), we can rewrite \( 2.25 \) as \( \frac{9}{4} \), thus \( (2.25)^{-\frac{1}{2}} = \left(\frac{9}{4}\right)^{-\frac{1}{2}} = \left(\frac{4}{9}\right)^{\frac{1}{2}} \). The square root of \( \frac{4}{9} \) is \( \frac{2}{3} \). Thus, the answer is \( \frac{2}{3} \).