5 * 7 = 37Math brain teasers require computations to solve.
According to basic algebra, (A + B)(A - B) is equal to A^2 - B^2 (A^2 is "A squared"). Substituting 1 for B, we get A^2 - 1^2.
A^2 - 1^2 is the same as A^2 + (-1^2). Since -1 times -1 is one, we end up with A^2 + 1.
If we substitute 6 for A, we get (6+1)(6-1) = 6^2+1, or 37. Since 6+1 is 7 and 6-1 is 5, five times seven is thirty-seven.
What's wrong with this proof?
AnswerA^2 - 1^2 is NOT the same as A^2 + (-1^2). It is actually A^2 + -(1^2), or the negative of 1 * 1.
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