Triangle ABCABCABC: a=5,b=7,c=8a = 5, b = 7, c = 8a=5,b=7,c=8. Using cosine rule, find cosA\cos AcosA.
12\frac{1}{2}21
815\frac{8}{15}158
1114\frac{11}{14}1411
34\frac{3}{4}43