In triangle with and , let be the midpoint of . Choose point on the extension of past and point on segment such that lies on . Let be on the opposite side of from such that and . Let intersect the circumcircle of again at , and let intersect the circumcircle of again at . Prove that ,, and are collinear.
If are complex numbers such that and if denotes the sum of all products of these numbers taken at a time, prove that whenever the denominator of the left-hand side is different from .