perplexus.info :: Just Math : Prime from absolute expression

Prime from absolute expression (Posted on 2024-09-21)

For how many integers x is |15x²-32x-28| a prime number?

No Solution Yet Submitted by Danish Ahmed Khan

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The quadratic factors: 15x^2-32x-28 = (3x-2)*(5x+14)

This is composite, so if an integer x evaluates to make |15x2-32x-28| prime then one of those factors is +/-1.

Of the four possible cases, two of them result in integer x. Those values are x=1 and x=-3.

Posted by Brian Smith on 2024-09-22 12:27:43

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