Which function has a removable discontinuity at x is equal to 7 ?

Factor the numerator in choice C: x² − 10x + 21 = (x − 3)(x − 7). For x ≠ 7, the factor x − 7 cancels, leaving f(x) = x − 3, but the original function is undefined at x = 7. That creates a hole, or removable discontinuity, so the correct choice is C, the fraction with numerator x² − 10x + 21 and denominator x − 7.

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