Which of the following expressions is equal to an odd integer for every integer ?
Solution
When , the values of the five expressions are 2014, 2018, 2017, 2018, 2019.
When , the values of the five expressions are 2011, 2019, 4034, 2021, 2021.
Only the fifth expression is odd for both of these choices of , so this must be the correct answer.
We note further that since 2017 is an odd integer and is always an even integer, then is always an odd integer, as required.
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