sin−1x+cos−1x=π2\sin^{-1} x + \cos^{-1} x = \tfrac{\pi}{2}sin−1x+cos−1x=2π; tan−1x+cot−1x=π2\tan^{-1} x + \cot^{-1} x = \tfrac{\pi}{2}tan−1x+cot−1x=2π.