Advanced Math practice question

Answer: A. a² + b²

(a − b)² = a² − 2ab + b². Adding 2ab cancels the middle term: a² + b².

Why the other answers are wrong

B. a² − b²

a² − b² is the product (a − b)(a + b), not this expression.

C. (a + b)²

(a + b)² = a² + 2ab + b² keeps a middle term; here it cancels.

D. a² + 4ab + b²

a² + 4ab + b² adds 2ab to (a + b)², not to (a − b)².

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