We will use the following Rules :
(R1) : sintheta=cos(pi/2-theta)(R1):sinθ=cos(π2−θ)
(R2) : cos^-1(costheta)=theta, theta in [o,pi](R2):cos−1(cosθ)=θ,θ∈[o,π]
(R3) : sin^-1(sintheta)=theta, theta in [-pi/2,pi/2](R3):sin−1(sinθ)=θ,θ∈[−π2,π2]
Let us note that, by
(R1), sin(pi/12)=cos(pi/2-pi/12)=cos(5pi/12)(R1),sin(π12)=cos(π2−π12)=cos(5π12)
So, cos^-1(sin(pi/12))=cos^-1(cos(5pi/12))cos−1(sin(π12))=cos−1(cos(5π12)), where,
5pi/12 in [0,pi]5π12∈[0,π], so, using (R2)(R2), we get,
cos^-1(cos(5pi/12))=5pi/12cos−1(cos(5π12))=5π12
Again, as 5pi/12 in [-pi/2,pi/2]5π12∈[−π2,π2], by (R3)(R3), we have,
sin^-1(sin(5pi/12))=5pi/12sin−1(sin(5π12))=5π12
Finally, sin^-1(sin(cos^-1(sin(pi/12))))=5pi/12sin−1(sin(cos−1(sin(π12))))=5π12.
Hope, this will be of Help! Enjoy Maths.!