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# Solve or NSolve doesn't give any solution in twelve hours

Posted 11 years ago
 I typed NSolve[((900/454) (1816000 E^(-200 t/681) (-1 + E^(1782 t/6583)))/    2673) <= 50, t]with an equality (50) or inequality (<=50), with Solve or NSolve, and wihin 12 hours I don't get a solution.What is wrong ?bilik.miloslav@wanadoo.fr
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Posted 11 years ago
 Many thanks, adding "Reals" solves the problem. I don't know Reduce or FindInstance and I will look, thx again for your hints.
Posted 11 years ago
 NSolve[((900/454) (1816000 E^(-200 t/681) (-1 + E^(1782 t/6583)))/2673) == 50, t, Reals](*{{t -> 0.1402163037}, {t -> 143.2657137}}*)Took about 40 seconds on my PC.For inequality, one is supposed to use Reduce[]. But it was taking long time on my end. You can also use FindInstance if you just want one solution:FindInstance[((900/454) (1816000 E^(-200 t/681) (-1 + E^(1782 t/6583)))/2673) <= 50, t](* {{t -> 0}} *)
Posted 11 years ago
 FindRoot[((900/454) (1816000 E^(-200 t/681) (-1 + E^(1782 t/6583)))/     2673) == 50, {t, 1}]{t -> 0.140216}returns almost immediately.  Since there are mulitple solutions, the one that you get will depend on the starting value you give to FindRoot.
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