To add or subtract expressions, expand them to make their denominators the same. Least common multiple of $\left(x-1\right)^{2}$ and $\left(x-1\right)\left(-x-1\right)$ is $\left(x+1\right)\left(x-1\right)^{2}$. Multiply $\frac{1}{\left(x-1\right)^{2}}$ times $\frac{x+1}{x+1}$. Multiply $\frac{x}{\left(x-1\right)\left(-x-1\right)}$ times $\frac{-\left(x-1\right)}{-\left(x-1\right)}$.
Since $\frac{x+1}{\left(x+1\right)\left(x-1\right)^{2}}$ and $\frac{x\left(-1\right)\left(x-1\right)}{\left(x+1\right)\left(x-1\right)^{2}}$ have the same denominator, subtract them by subtracting their numerators.
Multiply $\frac{1-x^{2}}{1+x^{2}}$ times $\frac{1+x^{2}}{\left(x+1\right)\left(x-1\right)^{2}}$ by multiplying numerator times numerator and denominator times denominator.
To add or subtract expressions, expand them to make their denominators the same. Least common multiple of $\left(x-1\right)^{2}$ and $\left(x-1\right)\left(-x-1\right)$ is $\left(x+1\right)\left(x-1\right)^{2}$. Multiply $\frac{1}{\left(x-1\right)^{2}}$ times $\frac{x+1}{x+1}$. Multiply $\frac{x}{\left(x-1\right)\left(-x-1\right)}$ times $\frac{-\left(x-1\right)}{-\left(x-1\right)}$.
Since $\frac{x+1}{\left(x+1\right)\left(x-1\right)^{2}}$ and $\frac{x\left(-1\right)\left(x-1\right)}{\left(x+1\right)\left(x-1\right)^{2}}$ have the same denominator, subtract them by subtracting their numerators.
Multiply $\frac{1-x^{2}}{1+x^{2}}$ times $\frac{1+x^{2}}{\left(x+1\right)\left(x-1\right)^{2}}$ by multiplying numerator times numerator and denominator times denominator.