Rewrite $ a^14-b^14 $ as:
$$ \color{blue}{ a^14-b^14 = (a^7)^2 - (b^7)^2 } $$Now we can apply the difference of squares formula.
$$ I^2 - II^2 = (I - II)(I + II) $$After putting $ I = a^7 $ and $ II = b^7 $ , we have:
$$ a^14-b^14 = (a^7)^2 - (b^7)^2 = ( a^7-b^7 ) ( a^7+b^7 ) $$