Advanced Math practice question

Answer: 9

4x² − 81 = (2x)² − 9², so a = 9.

Common wrong answers

If you answered 3

3² = 9, but the constant must square to 81: a = 9.

If you answered 81

81 is a², not a.

If you answered 40.5

a is found from a² = 81, not from halving 81.

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