4. You can only cancel factors common to the numerator and denominator. The error is in cancelling part of a term, not a factor.
The correct simplification is
.. (5x² -5)/(x² -1) = 5(x² -1)/(x² -1) = 5 . . . . . . . x ≠ ±1
wherein the factors (x² -1) are cancelled from numerator and denominator.