In triangle ABC, the median from vertex A is perpendicular to the median from vertex B. If the lengths of sides AC and BC are 6 and 7 respectively, then the length of side AB is<spanclass=′latex−bold′>(A)</span>17<spanclass=′latex−bold′>(B)</span>4<spanclass=′latex−bold′>(C)</span>421<spanclass=′latex−bold′>(D)</span>25<spanclass=′latex−bold′>(E)</span>441