How do you work out pascal's triangle binomial expansion with the equation being (a+b) 3

(a + b) ³

(a + b) (a + b) (a + b)

(a (a + b) + b (a + b)) (a + b)

(a (a) + a (b) + b (a) + b (b)) (a + b)

(a² + ab + ab + b²) (a + b)

(a² + 2ab + b²) (a + b)

a² (a + b) + 2ab (a + b) + b² (a + b)

a² (a) + a² (b) + 2ab (a) + 2ab (b) + b² (a) + b² (b)

a³ + a²b + 2a²b + 2ab² + ab² + b³

a³ + 3a²b + 3ab² + b³