(x+5)^3 = x^3 + 3x^25 + 3x5^2 + 5^3
(x+5)^3 = x^3 + 15x^2 + 75x + 125

(x-5)^3 = x^3 - 3x^25 + 3x5^2 - 5^3
(x-5)^3 = x^3 - 15x^2 + 75x - 125

(x+5)^3 + (x-5)^3 = (x^3 + 15x^2 + 75x + 125) + (x^3 - 15x^2 + 75x - 125)
(x+5)^3 + (x-5)^3 = 2x^3 + 150x