Advanced Math practice question

Answer: A. a²

(a − b)(a + b) = a² − b². Adding b² cancels the −b²: a² − b² + b² = a².

Why the other answers are wrong

B. a² − 2b²

a² − 2b² subtracts b² again instead of adding it.

C. a² + 2b²

a² + 2b² adds b² to a² + b², but the product is a² − b².

D. (a + b)²

(a + b)² = a² + 2ab + b², which contains a cross term the original never has.

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