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anonymous

  • 5 years ago

trapezoidal rule for uneven lengths?

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  1. anonymous
    • 5 years ago
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    how can i take the trapezoidal rule estimation for X's that are not the same in difference? for example: i have x and y values for 0,1, and 3, but not 2. how do i find the y value of 2?

  2. anonymous
    • 5 years ago
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    oh nvm

  3. amistre64
    • 5 years ago
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    usually there is an equation to follow.... can you be more specific?

  4. anonymous
    • 5 years ago
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    nvm about the NVM. there is no equation. im just given a table with x and y values.

  5. amistre64
    • 5 years ago
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    then for the trap rule, I would assume the best you can do is add up all the individual areas that they give you right?

  6. anonymous
    • 5 years ago
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    so youre saying i need to add to trapezoid rules?

  7. anonymous
    • 5 years ago
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    t = 0 1 3 4 7 8 9 L(t) = 120 156 176 126 150 80 0

  8. anonymous
    • 5 years ago
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    i need to find L(2)

  9. mathteacher1729
    • 5 years ago
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    Oh, so you're not even integrating, you're just trying to find what the function is when you evaluate it at a point which is not given. :)

  10. anonymous
    • 5 years ago
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    well for now yes, but i need to use the trapezoid sum rule to find the approximate area. thats what my problem says

  11. anonymous
    • 5 years ago
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    and without L(2) i'm left with an expression.

  12. anonymous
    • 5 years ago
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    as an answer

  13. amistre64
    • 5 years ago
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    is there a pattern you can detect?

  14. anonymous
    • 5 years ago
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    nope, its all random Y values

  15. amistre64
    • 5 years ago
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    if you cant determine L(2), then assume that the interval [1,3] is the base, and use the [L(1)+L(3)]/2 is the height

  16. anonymous
    • 5 years ago
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    i dont understand

  17. anonymous
    • 5 years ago
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    the question wants me to start from the first 4 hours, and that starts at time 0 right?

  18. amistre64
    • 5 years ago
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    the area of a trapezoid is the base times the average height. i would just calculate the area between 1 and 3 and add it into the rest of it

  19. amistre64
    • 5 years ago
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    your not going to get an exact number any way, the trap areas will see to that :)

  20. anonymous
    • 5 years ago
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    yeah .... hope this isnot on the AP test cause ima fail

  21. amistre64
    • 5 years ago
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    i got no idea when the first four hours area, I dont have the problem :)

  22. anonymous
    • 5 years ago
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    alright, well thx for helping!

  23. amistre64
    • 5 years ago
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    sure thing, if you wanna post the entire problem, then I might be able to discern it better :)

  24. anonymous
    • 5 years ago
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    ok lets do that

  25. anonymous
    • 5 years ago
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    Concert tickets went on sale at noon (t=0) and were sold out within 9 hours. the number of people in line waiting to buy tickets at time t is modeled by a twice differentiable function L for 0<=t <= 9. Use a trapezoial sum rule with 3 sub intervals to estimate the average number of people waiting in line during the first 4 hours that tickets were on sale. t = 0 1 3 4 7 8 9 L(t) = 120 156 176 126 150 80 0

  26. anonymous
    • 5 years ago
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    sorry the L(t) is mssed up

  27. anonymous
    • 5 years ago
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    wait nevermind is good

  28. amistre64
    • 5 years ago
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    for starters, take the interval [0,9] and subdivide it into 3 equal intervals [0,3] ;[3,6] ;[6,9] is what it wants you to do right? then you find the area for each trap made according to the value of the "endpoints" of each subinterval..

  29. anonymous
    • 5 years ago
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    oh wait, so i should take it for the WHOLE thing then divide by 3?

  30. anonymous
    • 5 years ago
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    well it says the first 4 hours of sale. not the whole 0-9 hours

  31. anonymous
    • 5 years ago
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    i was thinking it strts at time 0 and ends at time 3 so that gives me 4 hours since people start to get tickets at time 0

  32. amistre64
    • 5 years ago
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    like this....

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  33. anonymous
    • 5 years ago
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    yeah

  34. amistre64
    • 5 years ago
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    ..... yeah the first 4 hours. if anything plot all your points on a graph and connect the dots... then determine the heights of your intervals from that

  35. anonymous
    • 5 years ago
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    but the graph could have a decrease at 2 so it would not give me the right y value

  36. amistre64
    • 5 years ago
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    you cant get the "exact value" regardless, you just have to do the best with what you have.... you cant "create" data that doesnt exist..

  37. amistre64
    • 5 years ago
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    the trap rule is the "best guess" method anyways, so it wont be exact regardless of what you do :)

  38. anonymous
    • 5 years ago
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    mmm ok

  39. amistre64
    • 5 years ago
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    plot the points. connect the dots, take it where it leads you :)

  40. anonymous
    • 5 years ago
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    ok thx

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