Find all values of x in the interval [0, 2𝜋] that satisfy the equation. (Enter your answers as a comma-separated list.)

Question

14 + 7 cos(2x) = 21 cos(x)

Answer 1

14 + cos 2x = 21 cos x

cos 2x = 21 cos x - 14

2 cos² x - 1 = 21 cos x - 14

Set equal to zero and solve using Zereo Product Rule (Algebra 2)

Answer 2