## Elementary Geometry for College Students (7th Edition)

$a^{2}$ = $b^{2}$ + $c^{2}$ - 2bc cosα
Given the values of a,b and c We need to find the value of α By using the theorem 11.4.3 In triangle ABC $a^{2}$ = $b^{2}$ + $c^{2}$ - 2bc cosα