=(x-5)(x-8)(x-6)(x-7)-9
=(x^2-13x+40)(x^2-13x+42)-9
=(x^2-13x)^2+82(x^2-13x)+40*42-9
=(x^2-13x)^2+82(x^2-13x)+1671
\(=\left(x^2-13x\right)^2+82\left(x^2-13x\right)+1681-10\)
\(=\left(x^2-13x+41\right)^2-10\)
\(=\left(x^2-13x+41-\sqrt{10}\right)\left(x^2-13x+41+\sqrt{10}\right)\)