tan−1x+y1−xy\tan ^{-1} \frac{x+y}{1-x y}tan−11−xyx+y
tan−1x+y1−xy−π\tan ^{-1} \frac{x+y}{1-x y}-\pitan−11−xyx+y−π
tan−1x+y1−xy+π\tan ^{-1} \frac{x+y}{1-x y}+\pitan−11−xyx+y+π
tan−1x+y1−xy+π2\tan ^{-1} \frac{x+y}{1-x y}+\frac{\pi}{2}tan−11−xyx+y+2π