7cos2theta = 6
in the interval (0,2pi)
round to 3 decimals
7cos2θ = 6
cos2θ = 6/7
2θ = 31° or 329°
θ = 15.5° or 164.5°
since cos2θ has period 180°, add that to each of those values to get all solutions.
Oops. You also need to convert to radians.