Soal Matematika, Persamaan Kuadrat di-mix dengan Trigonometri.

x1 + x2 = -a
(x1+x2)² = a²
(sin 15 + cos 15)² = a²
a² = sin²15 + 2sin15cos15 + cos²15
a² = 1 + sin 30
a² = 1 + 1/2
a² = 3/2
a^4 = (a²)² = (3/2)² =9/4

x1 * x2 = b
sin 15 * cos 15 = b
(sin30)/2 = b
b = 1/4
b² = 1/16

a^4 -b² =9/4-1/16 = (36-1)/16 = 35/16 (C)

persamaan kuadrat

x² +ax + b = (x - sin 15)(x -cos 15)
x² + ax + b = x² - (sin 15 + cos 15)x + (sin 15. cos 15)
a = -sin 15 - cos 15)
a⁴ = ((- sin 15- cos 15)²)²
a⁴ = (1 + 2 sin 15 cos 15)²
a⁴ = (1+ sin 30)² = (1 +1/2)² = 9/4

b² = (sin 15 cos 15)² = {1/2 (2 sin 15 cos 15}²
b² = {1/2 sin 30}² = (1/4)² = 1/16

a⁴ - b² = 9/4 - 1/16 = (36 -1)/(16)= 35/16