Question 1200343
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For which values of n is the terms value equal to the sum of the terms to that point in the
the arithmetic sequence  7,5,3, . . . 
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<pre>
You are given first three terms of an arithmetic progression 7, 5, 3.


As you see, each next term is 2 units less than the previous term.


Using this rule, continue the sequence further

    7, 5, 3, 1, -1, -3, -5, -7, -9.


Now take the sum of written terms.


Do not worry: it is easy to calculate the sum, because in the sum 
the negative terms will kill the positive terms.


The only term, which will survive is the term -9.


So, the sum of this sequence is -9.


At the same time, the value of -9 is the 9-th term of the progression.


Doing this way, you just answered the problem's question:


    +---------------------- A N S W E R --------------------------+
    |      the value of "n" (the number of terms) when            |
    |    the sum of progression is equal to its n-th term, is 9.  |
    +-------------------------------------------------------------+
</pre>

Solved, answered and explained.