Multiply: 1−y1+y⋅1+y21−y2\frac{1-y}{1+y} \cdot \frac{1+y^2}{1-y^2}1+y1−y⋅1−y21+y2
11+y\frac{1}{1+y}1+y1
1−y1+y\frac{1-y}{1+y}1+y1−y
111
11−y\frac{1}{1-y}1−y1