Which of the following is an identity (true for all values where defined)?
x2−1x−1=x−1\frac{x^2 - 1}{x - 1} = x - 1x−1x2−1=x−1
x2−1x−1=x+1\frac{x^2 - 1}{x - 1} = x + 1x−1x2−1=x+1
x2−1x−1=x\frac{x^2 - 1}{x - 1} = xx−1x2−1=x
x2−1x−1=1x+1\frac{x^2 - 1}{x - 1} = \frac{1}{x + 1}x−1x2−1=x+11