(y + z)³
in expanded form: (y + z) (y + z) (y + z)
y(y + z) + z(y + z) 1st and 2nd set
y² + yz + yz + z² product of 1st and 2nd set
(y² + 2yz + z²)(y + z) multiply with 3rd set
y(y² + 2yz + z²) + z(y² + 2yz + z²)
y³ + 2y²z + yz² + y²z + 2yz² + z³
y³ + 2y²z + y²z + yz² + 2yz² + z³ Group like terms.
y³ + 3y²z + 3yz² + z³ Product of 1st, 2nd, and 3rd set ...2nd CHOICE