2x(x-2)(x^2 +1) = 2x(x^3 + x - 2x - 2) = 2x(x^3 - x - 2)

= 2x^4 - 2x^2 - 4x

(x+3)^2 - (x^2 - 36) = (x^2 + 6x + 9) - (x^2 - 36) = x^2 + 6x + 9 - x^2 + 36

= 6x + 45