2
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Solve was unable to solve the system with inexact coefficients or the system obtained by direct rationalization of inexact numbers present in the system. Since many of the methods used by Solve require exact input, providing Solve with an exact version of the system may help.

Solve[R - (20 (1 - (1 - exp[-0.692 R])^5))/exp[-0.692 R] == 0, R]
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closed as off-topic by Bob Hanlon, Artes, MarcoB, happy fish, george2079 May 6 '17 at 13:02

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  • "This question arises due to a simple mistake such as a trivial syntax error, incorrect capitalization, spelling mistake, or other typographical error and is unlikely to help any future visitors, or else it is easily found in the documentation." – Bob Hanlon, Artes, MarcoB, happy fish, george2079
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  • 2
    $\begingroup$ Solve[R - (20 (1 - (1 - Exp[-0.692 R])^5))/Exp[-0.692 R] == 0, R, Reals] says R->100. Same answer for NSolve. $\endgroup$ – bill s May 5 '17 at 22:55
  • $\begingroup$ Also, you used "exp" when you need to use "Exp[ ]". Got to capitalize the 'E'. $\endgroup$ – MikeY May 6 '17 at 1:09
  • $\begingroup$ note 100 is the exact limit solution as -k->Infinity, which is to say the solution to this problem is not "exactly" 100. You might do a second order series expansion if you wanted to chase that down. $\endgroup$ – george2079 May 6 '17 at 14:18