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Thread: Arithmetic progression

  1. #1
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    Arithmetic progression

    In an Arithmetic progression of n terms, the common differences is d and the last terms is l .how to find first two terms in d , l , n term?.....
    Is it use formula S_n=n/2(a+l) or S_n=n/2(2a+(n-1)d)?..i m confusing abt the way to solve...can anybody help me?

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  2. #2
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    Re: Arithmetic progression

    Term before last term = l-d
    2 terms before last term = l-2d
    .
    .
    .
    2nd term from beginning = l-(n-2)d
    1st term = l-(n-1)d
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  3. #3
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    Re: Arithmetic progression

    Quote Originally Posted by goldsomecriss View Post
    In an Arithmetic progression of n terms, the common differences is d and the last terms is l .how to find first two terms in d , l , n term?.....
    Is it use formula S_n=n/2(a+l) or S_n=n/2(2a+(n-1)d)?..i m confusing abt the way to solve...can anybody help me?
    This webpage contains a good summery or the formulas. The notation is a bit different.

    To your exact question: $S_n$ stands for the sum of every term in the progression.
    It is $\large S_n=\dfrac{n(a+\ell)}{2}=\dfrac{n}{2}(a+\ell)=n \dfrac {(a+\ell)}{2}$.
    In the formula, $a$ is the first term, $n$ is the number of terms, and $\ell$ is the last term.
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