Segitiga ABC AB=20cm AC=30cm Sudut B=30°.. Cos C =

[tex] \frac{20}{ \sin(c) } = \frac{30}{ \sin(30) } \\ \sin(c) = \frac{1}{3} \\ {sin}^{2} c + {cos}^{2} c = 1 \\ {cos}^{2} c = 1 - \frac{1}{9} \\ \cos(c) = \sqrt{ \frac{8}{9} } = \frac{2}{3} \sqrt{2} [/tex]