The locus of centroid of the triangle whose vertices are (acost, asint), (bsint, − bcost) and (1, 0), where t is a parameter is
a) (3x – 1)2 + (3y)2 = a2 – b2
b) (3x – 1)2 + (3y)2 = a2 + b2
c) (3x + 1)2 + (3y)2 = a2 + b2
d) (3x + 1)2 + (3y)2 = a2 – b2