Answer:
2π/3 + 2πn or 4π/3 + 2πn radians
Explanation:
Think of this as a quadratic function: replace the cos(x) with “x”.
2x^2 - 7x - 4 = 0
Now factor it
(2x + 1)(x - 4) = 0
Now, replace the “x” with cos(x) and solve
(2cos(x) + 1)(cos(x) - 4) = 0
2cos(x) + 1 = 0
cos(x) = -1/2
x = 2π/3 + 2πn or 4π/3 + 2πn radians
cos(x) = 4
x is undefined here