Hey there :)
( a + b )( a² - ab + b² )
Let us distribute ( a + b )
a ( a² ) + a ( - ab ) + a ( b² ) + b ( a² ) + b ( - ab ) + b ( b² )
a³ - a²b + ab² + a²b - ab² + b³
We can simplify further:
- a²b + a²b = 0
ab² - ab² = 0
a³ + b³
You can see in the picture I have attached that this is the 7th formula