Answer :
[tex]\sqrt[3]{9x^4}\cdot \sqrt[3]{3x^8}\implies \sqrt[3]{(9x^4)(3x^8)}\implies \sqrt[3]{27x^{4+8}}\implies \sqrt[3]{27x^{12}} \\\\\\ \sqrt[3]{3^3(x^4)^3}\implies 3x^4[/tex]
[tex]\sqrt[3]{9x^4}\cdot \sqrt[3]{3x^8}\implies \sqrt[3]{(9x^4)(3x^8)}\implies \sqrt[3]{27x^{4+8}}\implies \sqrt[3]{27x^{12}} \\\\\\ \sqrt[3]{3^3(x^4)^3}\implies 3x^4[/tex]