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King Group Title

:Help...........for how many positive integers n is n^3 -8n^2+20n-13 a prime number??

  • 2 years ago
  • 2 years ago

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  1. sheg Group Title
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    factorize it

    • 2 years ago
  2. King Group Title
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    how watever i get is not a prime number

    • 2 years ago
  3. King Group Title
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    why?

    • 2 years ago
  4. King Group Title
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    oh

    • 2 years ago
  5. King Group Title
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    but then ii have to plug in millions of values

    • 2 years ago
  6. sheg Group Title
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    what u want to calculate

    • 2 years ago
  7. sheg Group Title
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    (n^3 -8n^2+20n-13) a prime number

    • 2 years ago
  8. sheg Group Title
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    or n is a prime number

    • 2 years ago
  9. King Group Title
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    for n i will have to put millions of values to find how may n positive integers satisfy n^3 -8n^2+20n-13 to be a prime number

    • 2 years ago
  10. sheg Group Title
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    ok

    • 2 years ago
  11. King Group Title
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    so,what to do??

    • 2 years ago
  12. King Group Title
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    anything i can do to narrow down the possobilities

    • 2 years ago
  13. King Group Title
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    no answer given....

    • 2 years ago
  14. sheg Group Title
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    ok see for 2 it is prime number

    • 2 years ago
  15. sheg Group Title
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    wait i took wrong concept

    • 2 years ago
  16. sheg Group Title
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    \[(x-1) \times [(x-7)x + 13]\]

    • 2 years ago
  17. sheg Group Title
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    where x is n

    • 2 years ago
  18. King Group Title
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    ok

    • 2 years ago
  19. sheg Group Title
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    now see the first term is (x-1). and other than 2 no other even number is a prime number right

    • 2 years ago
  20. sheg Group Title
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    i got the answer

    • 2 years ago
  21. King Group Title
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    no n does not have to be a prime number n^3 -8n^2+20n-13 has to be a prime number

    • 2 years ago
  22. sheg Group Title
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    yeah i know (x−1)×[(x−7)x+13] it has to be prime

    • 2 years ago
  23. King Group Title
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    yup so x can be anything greater or equal to 2

    • 2 years ago
  24. sheg Group Title
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    first term is (x-1) and two is the only even prime number.

    • 2 years ago
  25. sheg Group Title
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    but if u will subtract 1 from any other prime number the resultant will be divisible by 2

    • 2 years ago
  26. sheg Group Title
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    getting my point or not

    • 2 years ago
  27. King Group Title
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    x can be 4

    • 2 years ago
  28. sheg Group Title
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    yeah u r right

    • 2 years ago
  29. sheg Group Title
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    it means that for any odd integer other than 3 u will not get a prime number

    • 2 years ago
  30. King Group Title
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    yeah

    • 2 years ago
  31. FoolForMath Group Title
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    Superb sheggy!

    • 2 years ago
  32. sheg Group Title
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    also the number cannot be graeter than 7

    • 2 years ago
  33. King Group Title
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    oh yeah

    • 2 years ago
  34. sheg Group Title
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    thanks fool bhai

    • 2 years ago
  35. sheg Group Title
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    so u are having a limited space to work out that is from 1 to 7

    • 2 years ago
  36. King Group Title
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    yes sheg u got it so answer is n=2,3,4

    • 2 years ago
  37. King Group Title
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    no actually 2 to 7

    • 2 years ago
  38. sheg Group Title
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    hahahaa right 2 to 7

    • 2 years ago
  39. sheg Group Title
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    but for 7 it will be 0

    • 2 years ago
  40. King Group Title
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    wait why cant it be greater than 7?

    • 2 years ago
  41. sheg Group Title
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    try any number u will get the answer

    • 2 years ago
  42. sheg Group Title
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    odd numbers cannot be included ok thats true

    • 2 years ago
  43. sheg Group Title
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    as i had told u any odd number subtracted by one will result in even number so it will be divisible by 2.........do u accept it or not

    • 2 years ago
  44. King Group Title
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    is 323 a prime number?

    • 2 years ago
  45. King Group Title
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    yeah i acept

    • 2 years ago
  46. King Group Title
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    its not div by 17

    • 2 years ago
  47. sheg Group Title
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    323 is divisible by 17

    • 2 years ago
  48. sheg Group Title
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    so 323 is not a prime number

    • 2 years ago
  49. King Group Title
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    4387 ?

    • 2 years ago
  50. sheg Group Title
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    what u have put x = ??

    • 2 years ago
  51. King Group Title
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    n=20

    • 2 years ago
  52. King Group Title
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    1443?

    • 2 years ago
  53. King Group Title
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    gtg shall come bak in 15 min

    • 2 years ago
  54. sheg Group Title
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    for n = 20 it should be equal to 5187

    • 2 years ago
  55. King Group Title
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    oh yeah 1443?

    • 2 years ago
  56. King Group Title
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    no

    • 2 years ago
  57. sheg Group Title
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    20^3 - 8*20^2 + 20*20 -13 =8000 - 3200 + 400 -13 = 8400 - 3213 = 5187

    • 2 years ago
  58. King Group Title
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    gtg cum bak in 15 mins

    • 2 years ago
  59. sheg Group Title
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    dear i had told u for no value greater than 7 it would fit

    • 2 years ago
  60. sheg Group Title
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    and both 1443 and 5187 is divisible by 3

    • 2 years ago
  61. King Group Title
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    i am bak so what to do now?

    • 2 years ago
  62. sheg Group Title
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    for no value greater than 7 that too even number it will not be a prime number

    • 2 years ago
  63. sheg Group Title
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    http://www.wolframalpha.com/input/?i=x^3-8x^2%2B20x-13+where+x+%3D+20 visit this website and plug in different value of x u will get the answer

    • 2 years ago
  64. sheg Group Title
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    king u there

    • 2 years ago
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