{x∈R:cos2x+2cos2x=2} is equal to
2nπ + π/3: n∈ Ζ
nπ±π/6: n∈ Ζ
nπ + π/3: n∈ Ζ
2nπ-π/3: n∈ Ζ
Given equation is
cos2x+2cos2x=2⇒2cos2x−1+2cos2x=2⇒4cos2x=3⇒cos2x=34⇒cos2x=cos2π6⇒x=nπ±π6:n∈Z