Final answer:
The common denominator for the complex fraction (1/a) -(1/b)/(1/a) +(1/b) is ab, which is found by multiplying the distinct denominators a and b.
Step-by-step explanation:
The common denominator for the complex fraction (1/a) -(1/b)/(1/a) +(1/b) can be determined by finding a common multiple of the denominators involved in the fraction. In this case, the denominators are a and b. To combine fractions, we need a common denominator, and that would be the product of the distinct denominators. Thus, the common denominator is indeed ab.
However, when dealing with the overall structure of this complex fraction, we are essentially looking at a single expression divided by another. Each expression (1/a) - (1/b) and (1/a) + (1/b) would require a common denominator, which is ab. Therefore, common denominator between these two expressions is still ab.