Question

What are the zeros of f(x)= 2 cos (3x) +1 on the interval [0,pi]

Answer 1

40° or 2π/9 rad

Explanation:

Let f(x) = 0 and solve

2cos (3x) + 1 = 0

2cos (3x) = -1

cos (3x) = -1/2

3x = arccos (-1/2) = 120

x = 40° or 2π/9 rad