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Correct answer: C. (4a + b)/(9a² − b²)
Add algebraic fractions by taking a common denominator and factorizing a difference of squares.
- Factorize 9a² − b² as (3a − b)(3a + b).
- Rewrite 1/(3a − b) with denominator 9a² − b²: 1/(3a − b) = (3a + b)/(9a² − b²).
- Now add: a/(9a² − b²) + (3a + b)/(9a² − b²) = (a + 3a + b)/(9a² − b²).
- Simplify the numerator: a + 3a + b = 4a + b.
- Therefore the result is (4a + b)/(9a² − b²).
- Restriction: 3a − b ≠ 0 and 3a + b ≠ 0.