Как решить неравенство: x^4-13x^2+36<0

\displaystyle x^4-13x^2+36=0\\\\x^2=t\\\\t^2-13t+36=0\\\\D=169-144=25=5^2\\\\t_{1.2}= \frac{13\pm 5}{2}\\\\t_1=4; t_2=9\\\\x^2=4; x=\pm 2 \\\\x^2=9; x=\pm 3