In triangle ABC, AB = 7, AC = 2, and BC = 8. Find cos(A).
AB = 7 ---> c = 7
AC = 2 ---> b = 2
BC = 8 ---> a = 8
Law of Cosines: a2 = b2 + c2 - 2·b·c·cos(A)
82 = 22 + 72 - 2·2·7·cos(A)
64 = 4 + 49 - 28·cos(A)
64 = 53 - 28·cos(A)
11 = - 28·cos(A)
-11/28 = cos(A)
