Cos(x+п/3)cos(x-п/3)-0.25=0

Question

Cos(x+п/3)cos(x-п/3)-0.25=0

Answer 1

1/2(cos2π/3+cos2x)=1/4
2*cos2π/3+2cos2x=1
2*(-1/2)+2cos2x=1
2cos2x=2
cos2x=1
2x=2πk,k∈z
x=πk,k∈z