+36916 Triangle bisector theorem
12/AD = 15/DC AC = sqrt 15^2 - 12^2 ) = 9 (Pythag theorem)
12/15 = AD/DC
4/5 = AD/DC
AD = 4/9 * 9 = 4 DC = 5/9 *9 = 5
BD = SQRT (12^2 + 4^2) = sqrt 160
Law of cosines:
15^2 = 5^5 + sqrt160^2- 2 * 5* sqrt160 cos BDC
cos BDC = - .31623 (if I made no mistakes....check my math !)
