(I)b and a are in the same direction, then b = k (2 2,0), and k > 0.

|b|=2k= 1，k= 1/2。

So b = (1, 0)

(2) b=(x, y)

a b = 2x = | a | | b | cos 120 = 2× 1×(- 1/2)=- 1

x=- 1/2

|b|？ =x？ +y？ = 1，y =∞3/2。

B = (- 1/2, ∨3/2) or B = (- 1/2, -∨ 3/2).

A+B = (3/2, ∞3/2) or (3/2, -3/2).