Is there a similar way to calculate the Σ summation formula in PHP or MySQL?

As shown in the picture: knowing N, find X. Thank you~

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As shown in the picture: knowing N, find X. Thank you~

PHPExcel has an IRR function to find the internal rate of return

PHP and MySQL (SQL statement) both have the sum() function.

First use the arithmetic sequence summation formula to simplify it, and then just pick any numerical algorithm for approximation.