Let:
[tex]y=x^2[/tex]Substitute into the equation:
[tex]y^2+y-20=0[/tex]The factors of -20 that sum to 1 are -4 and 5, so:
[tex](y-4)(y+5)=0[/tex]Split into 2 equations:
[tex]\begin{gathered} y-4=0_{\text{ }}(1) \\ y+5=0_{\text{ }}(2) \end{gathered}[/tex]Substitute back for:
[tex]y=x^2[/tex]For (1):
[tex]\begin{gathered} x^2-4=0 \\ x^2=4 \\ x=\sqrt[]{4} \\ x=\pm2 \end{gathered}[/tex]For (2):
[tex]\begin{gathered} x^2+5=0 \\ x^2=-5 \\ x=\sqrt[]{-5} \\ x=\pm\sqrt[]{5}i \end{gathered}[/tex]The solutions are:
[tex]\begin{gathered} 2 \\ -2 \\ i\sqrt[]{5} \\ -i\sqrt[]{5} \end{gathered}[/tex]