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    A sequence of numbers, u1,u2,u3....un,..... is given by the formula un= 3(2/3)^n -1 where n is a positive integer.
    a) Find u1, u2 and u3
    b) show that the sum of 15 un= -9.014 where n=1
    c) prove that u = 2(2/3)^n -1
    n+1
    please help with parts two and three!! i cant prove or show.... much appreciated :rolleyes:
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    (Original post by gingeninge)
    A sequence of numbers, u1,u2,u3....un,..... is given by the formula un= 3(2/3)^n -1 where n is a positive integer.
    a) Find u1, u2 and u3
    b) show that the sum of 15 un= -9.014 where n=1
    c) prove that u = 2(2/3)^n -1
    n+1
    please help with parts two and three!! i cant prove or show.... much appreciated :rolleyes:
    Is that \ u_n = 3(\frac{2}{3})^{n-1} or \3(\frac{2}{3})^n - 1?
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    (Original post by joostan)
    \3(\frac{2}{3})^n - 1?
    the latter of the two
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    (Original post by gingeninge)
    the latter of the two
    How good is your sigma manipulation?
    The original is the same as:
     S_n = \ 3 \displaystyle\sum_{r=1}^n (\frac{2}{3})^n - \displaystyle\sum_{r=1}^n 1
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    OMG how did i miss that! thank you so much :-) :-)
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    (Original post by gingeninge)
    OMG how did i miss that! thank you so much :-) :-)
    NP
 
 
 
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