\begin{array}{l} 0, 999 \dots = 0, 333 \dots + 0, 333 \dots + 0, 333 \dots = \\ = \frac{1}{3} + \frac{1}{3} + \frac{1}{3} = 1 \end{array}

${\begin{array}{l} 0,999 \ldots = 0,333 \ldots + 0,333 \ldots + 0,333 \ldots = \\ = \frac {1} {3} + \frac {1} {3} + \frac {1} {3} = 1 \end{array}}$

Error