Answer:
[tex]\sqrt[9]{a^{4}}[/tex]
Step-by-step explanation:
To convert a fraction form into a radical form you need to know that the denominator will be the root index and the numerator will be the exponent into the root. For the case of four ninths:
[tex]a^{\frac{4}{9}} = \sqrt[9]{a^{4}} .[/tex]
