perplexus.info :: Just Math : No integer roots

No integer roots (Posted on 2017-10-22)

Without solving the equation
15x^2-7y^2=9
explain why it has no integer roots.

No Solution Yet Submitted by Ady TZIDON

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The last digit of 15x^2 is 0 or 5.

The last digit of 7y^2 is (0,7,8,3,2,5,2,3,8,7) according as the last digit of y is (0,1,2,3,4,5,6,7,8,9).

In none of the cases is it possible for the last digit of the difference to equal 9.

Posted by xdog on 2017-10-22 17:42:51

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