[tex](x^2 - 5x - 20)^2 = (x^2 - 2x - 10)^2\\x^2-5x-20=x^2-2x-10 \vee x^2-5x-20=-x^2+2x+10\\\\\\x^2-5x-20=x^2-2x-10\\3x=-10 \\x=-\dfrac{10}{3}\\\\\\x^2-5x-20=-x^2+2x+10\\2x^2-7x-30=0\\2x^2+5x-12x-30=0\\x(2x+5)-6(2x+5)=0\\(x-6)(2x+5)=0\\x=6 \vee x=-\dfrac{5}{2}\\\\\\x\in\left\{-\dfrac{10}{3},-\dfrac{5}{2},6\right\}[/tex]
