Resposta :
[tex]A = \frac{1}{2} - \left [ 0,8 - \left ( 0,333... - \frac{1}{2} \right ) \right ] \\\\ A = \frac{1}{2} - \left [ \frac{8^{\div 2}}{10^{\div 2}} - \left ( \frac{3^{\div 3}}{9^{\div 3}} - \frac{1}{2} \right ) \right ] \\\\ A = \frac{1}{2} - \left [ \frac{4}{5} - \frac{1}{3} + \frac{1}{2} \right ] \\\\ A = \frac{1}{2} - \frac{4}{5} + \frac{1}{3} - \frac{1}{2} \\\\ A = \frac{1}{3} - \frac{4}{5} \\\\ A = \frac{5 - 12}{15} \\\\ A = \frac{- 7}{15} \\\\ \boxed{A = - 0,4\bar{6}}[/tex]