по формуле куб суммы двучлена
0;\\\\x^3+3*x^2*\sqrt{5}+3*x*(\sqrt{5})^2+(\sqrt{5})^3>0;\\\\(x+\sqrt{5})^3>0;\\\\x+\sqrt{5}>0;\\\\x>-\sqrt{5};\\\\(-\sqrt{5}; +\infty)" alt="x^3+3\sqrt{5}x^2+15x+5\sqrt{5}>0;\\\\x^3+3*x^2*\sqrt{5}+3*x*(\sqrt{5})^2+(\sqrt{5})^3>0;\\\\(x+\sqrt{5})^3>0;\\\\x+\sqrt{5}>0;\\\\x>-\sqrt{5};\\\\(-\sqrt{5}; +\infty)" align="absmiddle" class="latex-formula">