a³ + 3ab(a + b) + b³ = ____?

3(a + b)³

(a + b)³

(3a + 3b)³

None of these

The given expression is:

a³ + 3ab(a + b) + b³

Factor the expression:

(a + b)(a² - ab + b²) + 3ab(a + b)

Combine like terms:

(a + b)(a² - ab + b² + 3ab)

Simplify:

(a + b)(a² + 2ab + b²)

Recognize the perfect cube:

(a + b)³