Expanding the left side:

(x^2 + 3x - 2)(x^2 + 3x - 2) + 3(x^2 + 3x - 2)
= (x^4 + 3x^3 - 2x^2 + 3x^3 + 9x^2 - 6x - 2x^2 - 6x + 4) + 3x^2 + 9x - 6
= x^4 + 6x^3 + 7x^2 - 14x + 4 + 3x^2 + 9x - 6
= x^4 + 6x^3 + 10x^2 - 5x - 2

Therefore, the given equation becomes:

x^4 + 6x^3 + 10x^2 - 5x - 2 = x

Rearranging this equation to equal zero gives:

x^4 + 6x^3 + 10x^2 - 5x - 2 - x = 0
x^4 + 6x^3 + 10x^2 - 6x - 2 = 0

So, the final equation is x^4 + 6x^3 + 10x^2 - 6x - 2 = 0.