sebuah segitiga ABC panjang sisi AB=10 cm AC=15cm sudut B =30 derajat. nilai cos C?

Mapel : Matematika
Kelas : X SMA
Bab : Trigonometri

Pembahasan :
Aturan Sinus

AB/Sin C = AC/Sin B
10/Sin C = 15/Sin 30°
10 . Sin 30° = 15 . Sin C
10 . (1/2) = 15 . Sin C
5 = 15 Sin C
Sin C = 1/3

Identitas Trigonometri
Cos C = √[1 - (Sin C)²]
Cos C = √[1 - (1/3)²]
Cos C = √[1 - (1/9)]
Cos C = √[8/9]
Cos C = 2/3 √2