SOLUTION: how can i find the maximum partial sum of a decreasing arithmetic sequence?

Question 1000972: how can i find the maximum partial sum of a decreasing arithmetic sequence?
Answer by ikleyn(52790) (Show Source): You can put this solution on YOUR website!
.
- Write the formula for the sum of an arithmetic progression;

- substitute numerical values of and , the common difference;
- replace n, the number of the terms, by x;

- you will get the quadratic parabola function of x;

- find x0 where the maximum of this quadratic function is achieved (x-coordinate of the vertex);

- take n closest to x0.

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