tan−1x+y1−xy\tan ^{-1} \frac{x+y}{1-x y}tan−11−xyx+y
tan−1y+z1−yz\tan ^{-1} \frac{y+z}{1-y z}tan−11−yzy+z
tan−1x−y1+xy\tan ^{-1} \frac{x-y}{1+x y}tan−11+xyx−y
tan−1y−z1+yz\tan ^{-1} \frac{y-z}{1+y z}tan−11+yzy−z
