The range of the real valued function f(x)= f(x) =f(x)= sin−1(1+x22x)\sin^{-1} \left( \frac{1 + x^2}{2x} \right)sin−1(2x1+x2) +cos−1(2x1+x2)+ \cos^{-1} \left( \frac{2x}{1 + x^2} \right)+cos−1(1+x22x) is: