Jawab:
AB = 4 cm
AC = 6 cm
BC = 2√7 cm

Penjelasan dengan langkah-langkah:
Diketahui
AB (a) = (x - 1) cm
AC (b) = (x + 1) cm
BC (c) = 2√(x+2) cm
θ = 60°

Ditanya panjang sisi-sisinya

Gunakan aturan cosinus
c² = a² + b² - 2ab(cos θ)
(2√(x+2))² = (x-1)² + (x+1)² - 2(x-1)(x+1)(cos 60°)
2² · √(x+2)² = x²-2x+1 + x²+2x+1 - 2(x² - 1)(½)
4 (x+2) = x²+1 + x²+1 - (x² - 1)
4x + 8 = 2x² + 2 - x² + 1
4x + 8 = x² + 3
x² - 4x + 3 - 8 = 0
x² - 4x - 5 = 0
(x - 5)(x + 1) = 0
x = 5, x = -1 (tidak memenuhi)
x = 5

AB = (x - 1) cm = (5-1) cm = 4 cm
AC = (x + 1) cm = (5+1) cm = 6 cm
BC = 2√(x+2) cm = 2√(5+2) cm = 2√7 cm

(xcvi)