This equation is a polynomial equation in terms of x. To solve it, we need to expand the expressions and simplify.

Expanding the expressions:

(х^2- 25)^4 = (x^2 - 25)(x^2 - 25)(x^2 - 25)(x^2 - 25)
= (x^4 - 50x^2 + 625)(x^4 - 50x^2 + 625)
= x^8 - 100x^6 + 3050x^4 - 2500x^2 + 390625

(x^2 + 3x -10)^2 = (x^2 + 3x -10)(x^2 + 3x -10)
= (x^4 + 6x^3 - 10x^2 + 3x^3 + 18x^2 - 30x - 10x^2 - 30x + 100)
= x^4 + 9x^3 + 8x^2 - 60x + 100

Now we add both expressions:

x^8 - 100x^6 + 3050x^4 - 2500x^2 + 390625 + x^4 + 9x^3 + 8x^2 - 60x + 100

Combining like terms, we get:

x^8 -100x^6 + 3051x^4 + 9x^3 - 2492x^2 - 60x + 390725 = 0

This is the simplified form of the given equation.