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Math Help - Help getting a value from a graph.

  1. #1
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    Help getting a value from a graph.

    Hi.
    Like the topic says I need help getting a value from anywhere on a graph I made from a Sigma formula.
    The formula goes like this:
    0
    (Σ 50n)+100
    n=9
    Giving a start value off 100 and a final value off 2350.
    Each point on the graph would be the formula given with n=0-9
    Now comes the part where I have no idea what to do, or how to do it. I need to be able to find any value on that graph.
    So if I needed to find the value for 5,5 or 7,25 , what would I have to do?

    -Pus
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  2. #2
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    Re: Help getting a value from a graph.

    The sum is an arithmetic series. Do you know how to get the closed form of an arithmetic series?
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  3. #3
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    Re: Help getting a value from a graph.

    All I know os that the sum is calculated usimg a arithmetic progression that goes like (n(a1+an)/2
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  4. #4
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    Re: Help getting a value from a graph.

    OK good, so what will be the first term and the last term in your sequence that you are summing up?
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  5. #5
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    Re: Help getting a value from a graph.

    Now I'm not sure if it should be 0 and 9 , 0 and 2250 or 100 and 2350.
    But I think it equation would be 100 + (10((0+9)50))/2
    Where the 100 is just so it starts at 100 when the value is 0.
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  6. #6
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    Re: Help getting a value from a graph.

    Forget about the +100 for the moment. Just deal with the sum. What would be the first term in the sequence and what would be the last term?
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  7. #7
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    Re: Help getting a value from a graph.

    That would be 0 and 9 then I think.
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  8. #8
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    Re: Help getting a value from a graph.

    No, they would be the values of the counter. You are summing up the terms 50n, where the "n" is your counter.
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  9. #9
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    Re: Help getting a value from a graph.

    Ok, then the first and last term has to be 0 and 2250.
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  10. #10
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    Re: Help getting a value from a graph.

    Or is it:
    (10(050))/2
    and
    (10(950))/2
    ?
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  11. #11
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    Re: Help getting a value from a graph.

    The point Prove it was trying to make is that, since this is an arithmetic series (with 100 added), its sum, up to "n", is 50\frac{n(n+1)}{2}+ 100. To evaluate that at non-integers, such as 5.5 or 9.5, just use those numbers for n. When n= 5.5 that is 50\frac{5.5(6.5)}{2}+ 100= 50(17.875)+ 100= 17.875.
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  12. #12
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    Re: Help getting a value from a graph.

    Amazing, it looks like it works just like I wanted it to work. Thank you so much!
    And sorry for being bad at math. The last time I had math was the first year at high school. The rest I had to learn by myself.
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