(x^2 + 12)(x^2 - 2y)

(x^2 + 12) (x^2 - 2y)

(x^2)(x^2) (x^2)(-2y) (+12)(x^2) (+12)(-2y)

x^4 -2x^2y +12x^2 -24y

x^4 +12x^2 -2x^2y -24y