The identity (a − b)² is equal to:

Aa² − b²

Ba² − 2ab + b²

Ca² + 2ab + b²

Da² + ab − b²

Answer & Solution

Correct answer: B. a² − 2ab + b²

We have (a − b)² = (a − b)(a − b). That is (a − b)² = a² − ab − ba + b². So (a − b)² = a² − 2ab + b². The middle term is negative, distinguishing this from (a + b)².

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