To simplify this equation, let's first expand the squared terms:

(х^2 - 8)^2 = (х^2 - 8)(х^2 - 8)
= х^4 - 8х^2 - 8х^2 + 64
= х^4 - 16х^2 + 64

Now, we can rewrite the equation as follows:

(х^4 - 16х^2 + 64) + 4(х^2 - 8) - 5 = 0
х^4 - 16х^2 + 64 + 4х^2 - 32 - 5 = 0
х^4 - 16х^2 + 4х^2 + 64 - 32 - 5 = 0
х^4 - 12х^2 + 27 = 0

So, the simplified form of the equation is х^4 - 12х^2 + 27 = 0.