Simplify:

(a)$4^{\frac{3}{2}}$

(b)${27}^{-\frac{2}{3}}$

(c) ${625}^{-\frac{3}{4}}$

An expression$4^{\frac{3}{2}}$

To simplify the given expression

The power of the radical is the numerator of the exponent, $3$.
The index of the radical is the denominator of the exponent, $2$.

$4^{\frac{3}{2}}=\sqrt{4^3}$

$=({\sqrt{\left(2^2\right)})}^3$

$=2^3$

$=8$

An expression${27}^{-\frac{2}{3}}$

To simplify the given expression

By using the property, $a^{-n}=\frac{1}{a^n}$,

${27}^{-\frac{2}{3}}=\frac{1}{{27}^{{\displaystyle \frac{2}{3}}}}$

The power of the radical is the numerator of the exponent, $2$.
The index of the radical is the denominator of the exponent, $3$

${27}^{-\frac{2}{3}}=\frac{1}{{\left(\sqrt[3]{27}\right)}^2}$

$=\frac{1}{(\sqrt[3]{3^3{)}^2}}$

$=\frac{1}{3^2}$

$=\frac{1}{9}$

An expression${625}^{-\frac{3}{4}}$

To simplify the given expression

By using the property, $a^{-n}=\frac{1}{a^n}$,

${625}^{-\frac{3}{4}}=\frac{1}{{625}^{{\displaystyle \frac{3}{4}}}}$

The power of the radical is the numerator of the exponent, $3$.
The index of the radical is the denominator of the exponent, $4$.

${625}^{-\frac{3}{4}}=\frac{1}{{\left(\sqrt[4]{625}\right)}^3}$

$=\frac{1}{{\left(\sqrt[4]{5^4}\right)}^3}$

$=\frac{1}{5^3}$

$=\frac{1}{125}$