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Homework Help: Confused in graphs?

  1. Jul 8, 2011 #1
    Confused in graphs???

    1. The problem statement, all variables and given/known data
    My teacher gave a question in which he have to find the number of solutions:-
    [tex]10sin(x)=x[/tex]
    I solved it using the graphs and i got the number of solutions to be 4.
    But when i came back home and tried to do it on Microsoft Mathematics, i found the results to be completely different. Number of solutions came out to be 1.
    I think i have used some wrong statement in Microsoft Mathematics. Please someone tell me the correct statement.


    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Jul 8, 2011 #2

    eumyang

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    Re: Confused in graphs???

    I found MORE THAN four solutions, so it's not either 1 or 4.
     
  4. Jul 8, 2011 #3
    Re: Confused in graphs???

    Oops Sorry!! It's 7 but please solve my problem!!
     
  5. Jul 8, 2011 #4

    Mentallic

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    Re: Confused in graphs???

    Is your problem why Microsoft Mathematics gave you just 1 solution or how to find that there are 7 solutions?

    The program would've given you the smallest positive value for various reasons.
     
  6. Jul 8, 2011 #5
    Re: Confused in graphs???

    My problem is Microsoft Mathematics gave me only 1 solution. :frown:
     
  7. Jul 8, 2011 #6

    eumyang

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    Re: Confused in graphs???

    I downloaded the program, and now I see what you mean. I get the same issue. When I type this in the worksheet:
    nsolve({10 sin(x) = x},{x})
    I only get one solution of x ≈ 0. However, when I graph the two sides, the graphs do intersect 7 times. The only way I could get it to give me all solutions was to limit my range of x values and type the nsolve command 7 times.

    For the 2nd solution, I typed this:
    nsolve({10 sin(x) = x},{x,-10,-8})
    (the bolded indicates that the program should only look at x values between -10 and -8) and I got x ≈ -8.423.... I repeat this 5 more times, changing the range of x values (bolded) by looking at the graph each time. Eventually you'll get all 7 solutions. Very tedious. As today was the 1st time I ever used Microsoft Mathematics, maybe someone here who knows more could chime in.
     
  8. Jul 8, 2011 #7
    Re: Confused in graphs???

    Where to type this nsolve command? :confused:
    And where you typed this equation "nsolve({10 sin(x) = x},{x,-10,-8})".
    Please provide a screenshot.
     
  9. Jul 8, 2011 #8

    eumyang

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    Re: Confused in graphs???

    See attachment. I typed the command in the "Worksheet" tab. Also, on the top, I had already clicked the "Home" tab. Make sure that you are in Radian mode. This is using the latest version, 64-bit.
     

    Attached Files:

  10. Jul 9, 2011 #9
    Re: Confused in graphs???

    I got my answer but what does this -10 and -8 denote?
     
  11. Jul 9, 2011 #10

    eumyang

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    Re: Confused in graphs???

    Please re-read 1st post (#6 in this thread). If you look at the graph, you will see that, going from left to right, the first time the two graphs intersect is somewhere between x = -10 and x = -8.

    The next time the graphs intersect is somewhere between x = -8 and x = -6, so I would type this to find the next solution:
    nsolve({10 sin(x) = x},{x,-8,-6})

    And so on.
     
  12. Jul 9, 2011 #11
    Re: Confused in graphs???

    But what does this mean "x ≈ -8.423...."?
     
  13. Jul 9, 2011 #12

    eumyang

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    Re: Confused in graphs???

    That's one of the 7 solutions to your equation. For whatever reason that I don't understand, in MS Mathematics we are not able to get all 7 solutions at once. That's why I said that you'll have to enter the nsolve command 7 times, changing the range of x-values each time, so that you can get all of the solutions.

    This command that I wrote previously:
    nsolve({10 sin(x) = x},{x,-8,-6})
    more or less is telling the program to ONLY look at x-values between -8 and -6 and state the x-value that makes the equation true.
     
  14. Jul 9, 2011 #13
    Re: Confused in graphs???

    Thanks for paying attention to this thread!! :smile:
    (I think i need to learn more about this program)
     
  15. Jul 9, 2011 #14

    I like Serena

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    Re: Confused in graphs???

    Are you already aware of Wolfram Alpha?
    That one does not give you the misleading surprise that you only get 1 solution, when there are more.

    See this link:
    http://www.wolframalpha.com/input/?i=10sin+x=x
     
  16. Jul 9, 2011 #15
    Re: Confused in graphs???

    I know about Wolfram Alpha.
     
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