5π/3
7π/6
π/3
π/6
cos−1(−sin7π6)=cos−1{cos(π2+7π6)} cos−1(cos5π3)=cos−1{cos(2π−5π3)} =cos−1(cosπ3)=π3 Remember, cos−1(cos x)=x, if 0≤x≤π
The principal value of cos−1cos7π6 is