The point O is the center of the circle circumscribed of the acute triangle ABC, and H is the point of intersection of the heights of this triangle. Let A1,B1,C1 be the points diametrically opposed to the vertices A,B,C respectively of the triangle, and A2,B2,C2 be the midpoints of the segments [AH],[BH]¸[CH] respectively . Prove that the lines A1A2,B1B2,C1C2 are concurrent . geometrycircumcircleorthocenterconcurrencyconcurrent