[latex]x^{4} -13 x^{2} +36=0

[latex]x^{4}-13x^{2}+36=0\\ x^{2}=t\\ t^{2}-13t+36=0\\ t_{1}=9\\ t_{2}=4\\ x^{2}=9\\ x=3;x=-3;\\ x^{2}=4\\ x=2;x=-2;[/latex] Ответ: -2, 2, -3, 3.