1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

A -ve number greater than infinity?

  1. Jun 24, 2006 #1
    Please follow the following arguments.
    5/3=1.66
    5/2=2.5
    5/1=5
    5/0.5=10
    .....
    ....
    5/0=infinity
    and then 5/(-1)= -5
    What you see? As the denominator is decreased the right hand side answer increases. The denominator becomes 3 then 2,then 1, then 0,then -1 ; and the answer increases, therefore -5 must be grater than infinity.
    Where's the flaw. Please illustrate.
     
  2. jcsd
  3. Jun 24, 2006 #2
  4. Jun 24, 2006 #3

    matt grime

    User Avatar
    Science Advisor
    Homework Helper

    In assuming that because for some set of values f(x) is increasing it is always increasing.
     
  5. Jun 24, 2006 #4

    AKG

    User Avatar
    Science Advisor
    Homework Helper

    Mainly, your answer doesn't work because 5 is a prime number.
     
  6. Jun 24, 2006 #5
    As one divides by smaller and smaller numbers, the output figure approaches but does not reach infinity, no?
     
  7. Jun 24, 2006 #6

    arildno

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    Dearly Missed

    Depends on your notion of smallness.
     
  8. Jun 25, 2006 #7
    Please follow the following arguments.

    5=5
    4=4
    3=3
    2=2
    1=1
    0=0
    -1=-1

    What do you see? As the left hand side decreases, the right hand side is greater than or equal to zero. Therefore, -1 must be greater than or equal to zero.

    Ja?

    Just because a property holds true for a certain range of numbers, it doesn't mean the pattern will follow for numbers outside that range. That's the flaw.
     
  9. Jun 28, 2006 #8

    Gokul43201

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    :rofl: :rofl: That's funny.
     
  10. Jun 28, 2006 #9
    It is? :confused:
     
  11. Jun 28, 2006 #10
    Ya, its funny because AKG's answer isn't right.
    ja ja
     
  12. Jun 29, 2006 #11
    5/0 does not equal infinity. The limit of 5/x as x approaches 0 equals inifinty.
     
  13. Jun 29, 2006 #12

    TD

    User Avatar
    Homework Helper

    In absolute value, yes. But else you have to mind the sign, depending on whether you're approaching 0 from the left or right, you get -inf resp. +inf.
     
  14. Jul 3, 2006 #13
    I don't see how you can say that -1 is greater than or equal to 0. I might be horribly wrong but what I think you're doing is just equating numbers & two equal numbers are always equal .. under no circumstances can be greater than or equal to.

    Look at this order:

    1=1
    9=9
    8=8
    -1=-1

    Don't you see?
     
  15. Jul 4, 2006 #14

    DaveC426913

    User Avatar
    Gold Member

    Albert:

    Please follow the following arguments.
    (x^2=y)
    3^2=9
    2^2=4
    1^2=1
    0^2=0
    -1^2=1

    What you see? As the x value is decreased, the y value (right hand side answer) decreases. The x value becomes 3 then 2,then 1, then 0,then -1 ; and the answer (y) decreases, therefore 1 must be less than zero.

    Now where's the flaw?


    (Hint: the only flaw is the conclusion that a given function must result in a straight and continuous line.)
     
    Last edited: Jul 4, 2006
  16. Jul 6, 2006 #15
    Okay...let me try to hit this topic.
    Graphing 5/x you will have a line that going from negative infinity to positive infinity it ALWAYS DECREASES. it never increases. However, it starts out negative and ends up positive.

    Lesson learned today: Don't mess with the division by zero.
     
  17. Jul 6, 2006 #16
    No you do not have a line. You have a hyperbola in the first and third quandrants of the cartesian plane.
     
  18. Jul 8, 2006 #17
    Here am a graph of 1/x.
    http://www.mathsrevision.net/gcse/1overx.gif [Broken]
    5/x follows the same pattern.
     
    Last edited by a moderator: May 2, 2017
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook