Advanced MathHardDifference of squares as mental arithmetic
Advanced Math practice question
Using the identity a² − b² = (a − b)(a + b), what is the value of 73² − 27²?
Answer: 4600
73² − 27² = (73 − 27)(73 + 27) = 46 · 100 = 4600.
Common wrong answers
- If you answered 46
- 46 is only the factor 73 − 27; multiply by 100.
- If you answered 100
- 100 is only the factor 73 + 27; multiply by 46.
- If you answered 2116
- 2116 is 46², not the product 46 · 100.
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