\[- 3,5;\ - 3,7;\ldots \Longrightarrow d = - 0,2;\ \ \ \ \]
\[S_{n} = \frac{2a_{1} + (n - 1)d}{2} \cdot n\]
\[S_{29} =\]
\[= \frac{2 \cdot ( - 3,5) + 28 \cdot ( - 0,2)}{2} \cdot 29 =\]
\[= \frac{- 7 - 5,6}{2} \cdot 2,9 = - \frac{12,6}{2} \cdot 29 =\]
\[= - 6,3 \cdot 29 = - 182,7\]
\[S_{29} = - 182,7.\]