There is a point of discontinuity at x = b because the denominator has the factor x – b. There are points of discontinuity at both x = – b and x = b because the numerator has factors of x + b and x – b. There is a point of discontinuity at x = b only because the factor of x – b is common to both the numerator and denominator. There is a point of discontinuity at x = –b only because the factor of x – b is common to both the numerator and denominator and factors out.