tolong bantuin disertai caranya ya :) thanks..

Aturan Cosinus

ΔABC ,
a=6
b = 6
c = 6√2

cos C = (a²+b²- c²)/(2 a b)
cos C = (6² +6² - (6√2)²) /(2)(6)(6)
cos C = (36+36 - 72) /(72)
cos C = 0/72 = 0

Ingat rumus:
c² = a² + b² - 2ab.cosC

Diketahui:
a = 6 cm
b = 6 cm
c = 6√2 cm

Ditanya:
cosC = ?????

Jawab:
c² = a² + b² - 2ab.cosC
(6√2)² = 6² + 6² - 2(6)(6).cosC
72 = 36 + 36 - 72.cosC
72 = 72 - 72.cosC
72.cosC = 72 - 72
72.cosC = 0
cosC = 0/72
cosC = 0 (A)