Question

Jika sin teta - 2 cos teta = 0, tentukam cos 2 teta. Helppp T_T

Answer 1

Verified answer

Bab Trigonometri
Matematika SMA Kelas X

sin θ - 2 cos θ = 0
sin θ = 2 cos θ
sin θ / cos θ = 2
tan θ = 2
y/x = 2/1

r = √(x² + y²)
  = √(1² + 2²)
  = √(1 + 4)
  = √5

cos 2θ = cos² θ - sin² θ 
           = (x/r)² - (y/r)²
           = (1/√5)² - (2/√5)²
           = 1/5 - 4/5
          = -3/5