For two distinct fixed points A(a1,b1) and B(a2,b2), a point P(x,y) moves so that the area of △APB is a non–zero constant k square units.
(i) Obtain the equation representing the locus of P.
(ii) Prove that the locus consists of two straight lines parallel to the line AB.
(iii) Express the distance between these two lines in terms of k and the length AB.
(iv) What change occurs in the locus when k=0? Justify your answer.