Řeš v \( \mathbb{R} \) rovnici: \( \frac{\left(x^{2}-9\right)}{x^{2}+2 x-3}=0 \)
\( K=\{3\} \)
\( K=\{-3\} \)
\( K=\{0\} \)
\( K=\{\} \)
