The value of cos−1⁡(cos⁡10), is

We know that cos−1⁡(cos⁡θ)=θ, if 0≤θ≤πHere, θ=10 radiansClearly, it does not lie between O and π However (4π-10) between O and π such that cos (4π-10)=cos 10∴ cos−1⁡(cos⁡10)=cos−1⁡(cos⁡(4π−10))=4π−10