Bagaimana cara dan yg mana jawabannya

a² = b² + c² - 2bc cos A
a² = 3² + 2² - 2.3.2 cos 60˚
a² = 13 - 12.1/2
a² = 13 - 6
a² = 7
a = √7

c² = a² + b² - 2ab cos C
2² = (√7)²+ 3² - 2 . √7 . 3 cos C
4 = 7 + 9 - 6√7 cos C
6√7 cos C = 12
cos C = 12/6√7
cos C = 2/√7
cos C = 2/7 . √7 .........B