Step 1 :
Factor out common factor $ \color{blue}{ a^2 } $:
$$ a^8-a^2b^6 = a^2 ( a^6-b^6 ) $$Step 2 :
Rewrite $ a^6-b^6 $ as:
$$ \color{blue}{ a^6-b^6 = (a^3)^2 - (b^3)^2 } $$Now we can apply the difference of squares formula.
$$ I^2 - II^2 = (I - II)(I + II) $$After putting $ I = a^3 $ and $ II = b^3 $ , we have:
$$ a^6-b^6 = (a^3)^2 - (b^3)^2 = ( a^3-b^3 ) ( a^3+b^3 ) $$Step 3 :
To factor $ a^{3}+b^{3} $ we can use sum of cubes formula:
$$ I^3 + II^3 = (I + II) (I^2 - I \cdot II + II^2)$$After putting $ I = a $ and $ II = b $ , we have:
$$ a^{3}+b^{3} = ( a+b ) ( a^{2}-ab+b^{2} ) $$Step 4 :
To factor $ a^{3}-b^{3} $ we can use difference of cubes formula:
$$ I^3 - II^3 = (I - II) (I^2 + I \cdot II + II^2) $$After putting $ I = a $ and $ II = b $ , we have:
$$ a^{3}-b^{3} = ( a-b ) ( a^{2}+ab+b^{2} ) $$