[tex]\begin{gathered} c^2=b^2+a^2 \\ a^2=c^2-b^2 \\ a=\sqrt[]{c^2-b^2} \\ a=\text{ }\sqrt[]{9^2-3^2} \\ a=\text{ }\sqrt[]{81^{}-9^{}} \\ a=\text{ }\sqrt[]{72} \\ a=\text{ 6}\sqrt[]{2}\text{=8,48} \\ \text{the answer is a = 8,48 units} \end{gathered}[/tex]
