y = 2 sin(2/3πx+π/6)= 2cos(2/3πx+π/6-π/2)= 2cos[2/3π(x- 1/2)]

After moving its image to the left by 1/2 units, the obtained image coincides with the image of function y=2cos2π/3x.

So a= 1/2,

So vector a = (1, 2), vector b = (-4, 3),

|a|=√5，|b|=5，

The coordinates of the unit vector with the same included angle with vectors A and B are: (√5/5, 2√5/5), (-4/5, 3/5).

a * b = 1 *(4)+2 * 3 = 2，cos & lta，b & gt=a*b/|a|*|b|=2√5/5 .