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Math Help - Quadratic Sequences!

  1. #1
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    Quadratic Sequences!

    Work out an nth term formula for the triangular numbers 1,3,6,10,15,21,...

    Thanks in advance.
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  2. #2
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    Hello,
    Quote Originally Posted by suhaster View Post
    Work out an nth term formula for the triangular numbers 1,3,6,10,15,21,...

    Thanks in advance.
    Please note the pattern :

    \begin{array}{|c||c|c} \text{Rank }(n) & a_n & \text{Difference with the previous term} \\ \hline<br />
1 & 1 & \emptyset \\<br />
2 & 3 & 2=n \\<br />
3 & 6 & 3=n \\<br />
4 & 10 & 4=n \\<br />
5 & 15 & 5=n \end{array}

    So, what is a_{n}-a_{n-1} ?
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  3. #3
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    T_n  = \sum\limits_{k = 1}^n k
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  4. #4
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    Sorry to both of u but im not understanding what ur trying to say, can u tell me the answer and with it the explanation plz thats the best way of learning it for me. tar
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