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Quadratic expression integer iterations

  1. Apr 13, 2017 #1
    Why is the quadratic expression 20*x^2-1 only divisible by decimal numbers ending in -1 , or ending in -9 ?
    Sorry! My profile is a semi-retired carer.Location London(South) . Male 59. Have rudimentary maths -interests Number Theory , Prime Numbers.
     
    Last edited: Apr 13, 2017
  2. jcsd
  3. Apr 13, 2017 #2

    DrClaude

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    Staff: Mentor

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