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Homework Help: Please help me out

  1. Apr 7, 2006 #1
    [tex]2a \sum (2x_i)^2 + 2b \sum x_i - 2 \sum x_i y_i [/tex] I need to set it equal to zero and solve for a.

    [tex] 2a \sum x_i + 2nb - 2\sum y_i [/tex]

    and solve for b.

    I need a hint so i can start doing it, it confuses me all those adding symbols.

    The Answer the book came up with is:

    [tex] a= \frac{(n\sum x_i y_i - \sum x_i \sum y_i)} {(n \sum (x_i)^2 - (\sum x_i)^2} [/tex]

    [tex] b= \frac{1 / n} (\sum y_i - a \sum x_i) [/tex]
    Last edited: Apr 7, 2006
  2. jcsd
  3. Apr 7, 2006 #2


    User Avatar

    Staff: Mentor

    First of all, these look like simple algebraic manipulations. a and b are not inside any of the summations, so solving for them is straightforward. The solution for b looks fine (simple re-ordering of the equation), but the answer for a looks wrong. like, where did the n come from? Could that be the answer to a different question or something?

    Do the 2nd one first to see how easy it is. Then re-check the first problem statement and answer to be sure you have them synchronized.
  4. Apr 8, 2006 #3

    Thank you for your help!!!
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