Answer: [tex]p^-^\frac{1}{3}[/tex]
[tex]\sqrt[21]{\frac{p^-^4}{p^3} }[/tex]
[tex]\sqrt[21]{p^-^4^-^3}[/tex]
[tex]\sqrt[21]{p^-^7}[/tex]
[tex]\sqrt[21]{\frac{1}{p^7}}[/tex]
[tex]\frac{\sqrt[21]{1} }{\sqrt[21]{p^7} }[/tex]
[tex]\frac{1}{p^\frac{7}{21} }=\frac{1}{p^\frac{1}{3} }=p^-^\frac{1}{3}[/tex]
