2x1+x2\frac{2 x}{1+x^{2}}1+x22x
1−x21+x2\frac{1-\mathrm{x}^{2}}{1+\mathrm{x}^{2}}1+x21−x2
2x1−x2\frac{2 x}{1-x^{2}}1−x22x
2x2 x2x