Let △ABC have vertices A(a,2), B(3,b) and C(5,7). It is known that the area of the triangle is 6 square units.
(i) Form an equation in a and b using the given information.
(ii) If a=1, determine all possible values of b.
(iii) For each value of b obtained in part (ii), decide whether △ABC is acute–angled, right–angled or obtuse–angled. Justify your answer by calculating the squares of its side lengths.