(c)
Given, $f(x) = \frac{1}{2} - \tan{\left( \frac{\pi x}{2} \right),\ - 1 < x < 1}$
Given, domain of $f(x)$ is $d_{1} = ( - 1,\ 1)$
For domain of $g(x),\ 3 + 4x - 4x^{2} \geq 0$
$\Rightarrow \ \ \ \ \ \ \ \ \ \ \ \ (2x - 3)(2x + 1) \leq 0$
$\therefore$ Domain of $g(x)$ is $d_{2} = \left\lbrack - \frac{1}{2},\ \frac{3}{2} \right\rbrack$
Hence, domain of $(f + g) = d_{1} \cap d_{2} = \left\lbrack - \frac{1}{2},\ 1 \right\rbrack$