First lets solve the first part.
(a + b) (a - b) = a² - ab + ab - b²
= a² - b² (the - ab and the + ab cancel each other out)
Now lets solve:
(a² - b²) (a + b) = a³ + a²b - ab² - b³
Finally, use this and solve:
(a³ + a²b - ab² - b³) (a - b)
= [tex] a^{4} [/tex] - a³b + a³b - a²b² - a²b² + ab³ - ab³ + [tex] b^{4} [/tex]
= [tex] a^{4} [/tex] - 2a²b² + [tex] b^{4} [/tex]
