Jawab:
(d)  5

Penjelasan :
Diketahui
Segitiga besar
a = 7, b = 10, c = 11

Ditanya x

Pake cos rule
c² = a² + b² - 2ab cosθ
11² = 7² + 10² - 2(7)(10) cosθ
121 = 49+100 - 140 cosθ
140 cosθ = 49+100-121
140 cosθ = 28
cos θ = 28/140
cos θ = 1/5

Sisi segitiga kecil
c = x, a = 7-x, b = x
Pake cos rule
c² = a² + b² - 2ab cosθ
x² = (7-x)² + x² - 2(7-x)(x) (1/5)
x² = 49-14x+x² + x² - (2x(7-x) (1/5))
x² = 49-14x+x² + x² - [(14x - 2x²) (1/5)]
x² = 2x² - 14x + 49 - [(14x - 2x²) (1/5)]
5x² = 10x² - 70x + 245 - (14x - 2x²)
5x² = 10x² - 70x + 245 - 14x + 2x²
10x² + 2x² - 5x² - 70x - 14x + 245 = 0
7x² - 84x + 245 = 0 (:7)
x² - 12x + 35 = 0
(x-5)(x-7) = 0
x = 5, x = 7

x tidak sama dgn 7 krn panjang a
pd segitiga besar = 7, maka
x = 5

(d)  5
(xcvi)