\[a^{2}x^{2} + 2ax - 3 = 0;\ \ \ x = \frac{1}{2}\]
\[a^{2} \cdot \left( \frac{1}{2} \right)^{2} + 2a \cdot \frac{1}{2} - 3 = 0\]
\[\frac{1}{4}a² + a - 3 = 0\ \ | \cdot 4\]
\[a^{2} + 4a - 12 = 0\]
\[D = 4^{2} - 4 \cdot 1 \cdot ( - 12) =\]
\[= 16 + 48 = 64\]
\[a_{1} = \frac{- 4 + \sqrt{64}}{2 \cdot 1} = \frac{- 4 + 8}{2} =\]
\[= \frac{4}{2} = 2;\]
\[a_{2} = \frac{- 4 - \sqrt{64}}{2 \cdot 1} = \frac{- 4 - 8}{2} =\]
\[= \frac{- 12}{2} = - 6.\]
\[Ответ:при\ a = 2;\ a = - 6.\]