c) \( \left(\frac{a}{3}-3\right) \cdot\left(\frac{a}{3}+3\right)=0 \)

Solve the equation \( \left(\frac{a}{3}-3\right) \cdot\left(\frac{a}{3}+3\right)=0 \). Solve the quadratic equation by following steps: - step0: Solve using square roots: \(\left(\frac{a}{3}-3\right)\left(\frac{a}{3}+3\right)=0\) - step1: Multiply the terms: \(\frac{\left(a-9\right)\left(a+9\right)}{9}=0\) - step2: Multiply both sides: \(\left(a-9\right)\left(a+9\right)=0\) - step3: Expand the expression: \(a^{2}-81=0\) - step4: Add or subtract both sides: \(a^{2}=81\) - step5: Simplify the expression: \(a=\pm \sqrt{81}\) - step6: Simplify the expression: \(a=\pm 9\) - step7: Separate into possible cases: \(\begin{align}&a=9\\&a=-9\end{align}\) - step8: Rewrite: \(a_{1}=-9,a_{2}=9\) A equação \( \left(\frac{a}{3}-3\right) \cdot\left(\frac{a}{3}+3\right)=0 \) tem duas soluções: \( a=-9 \) e \( a=9 \).