## Elementary Geometry for College Students (6th Edition)

$b^{2}$ = $a^{2}$ + $c^{2}$ - 2ac cos β
We know the values of a,c, β We need to find the value of b By using theorem 11.4.3 $b^{2}$ = $a^{2}$ + $c^{2}$ - 2ac cos β