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    Σ(x-150)² = 7698
    Σ(x-150) = 216

    how would you get the first equation to equal Σx² = the answer
    and the second one to equal Σx = the answer

    thanks
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    (Original post by OmarAl)
    Σ(x-150)² = 7698
    Σ(x-150) = 216

    how would you get the first equation to equal Σx² = the answer
    and the second one to equal Σx = the answer

    thanks
    Try using some of the identities below to obtain one of the equations from the other. You can let (x-150) be r so that you can use eqn (a) to find n and then put the values of r and n into eqn (b). That's how I think you can get your first eqn using the second eqn. I'm not too sure about this method but see how it works.
    (a)n∑r=1 (r) =n(n+1)/2
    (b)n∑r=1( r^2) =n(n+1)(2n+1)/6
    (c)n∑r=1 (r^3) =(n(n+1)/2)^2
 
 
 
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