Find all integer x such that the expression x x − 3 x + 2 is an integer.
Type your answer as the sum of all solutions.
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Since x is an integer, x doesn't have any negative values. Hence you can ignore -1 and -2.
I think the answer should be 3 , with solutions − 2 , 1 , 4 . (But would probably be better if you specified "positive integer" instead.
It's an integer iff ( 1 + x 2 ) x is an integer. This occurs when, x in an integer and so is x 2 , e.g x = 1 , 4 . Or when ( 1 + x 2 ) = 0 . In this case x = 2 i and is an imaginary number.
Also note, x x − 3 x + 2 = x ( x − 1 ) ( x − 2 ) = y ( y − 1 ) ( y − 2 ) . Which is 0 when y = 1 , 2 .
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x x − 3 x + 2 = x − 3 + x 2
For this to be an integer, x must be a perfect square and x must divide 2
Factors of 2 : 1 , 2 , − 1 , − 2
So, x = 1 , 2 , − 1 , − 2 or x = 1 , 4
Answer is sum of values of x , that is, 5