Triangular numbers

Created by Eduan van der Walt Office Practice ( N4 )

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    Eduan van der Walt 2016-10-19

    Show that :

    The sum 1+9+9^2+9^3+9^4...+9^k is always a triangular number

Answers


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    Brendon Taljaard 2016-10-19

    This is a finite geometric series with sum = XXXXX which is triangular.

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    Eduan van der Walt 2016-10-19

    Bravo! Congratulations! 
    You got it! 
    Anyway there 100`s ways to compute the sum of consecutive integers (1,2,3,....n)
    I will post them one day with the method on how to find such closed formulas.

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    Brendon Taljaard 2016-10-19

    Be careful!

    1+9+92++9k1+9+92+⋯+9k is a triangular number for all kk.

    However all triangular numbers are not of this form.

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    Brendon Taljaard 2017-02-14

    Toest

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    Brendon Taljaard 2017-02-14

    sdfsdfsdfsdf

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    Eduan van der Walt 2017-02-19

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