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 2017-02-22 05:59:17 +0100 received badge ● Good Question (source) 2017-01-17 11:26:33 +0100 received badge ● Notable Question (source) 2016-03-06 09:09:01 +0100 received badge ● Famous Question (source) 2014-12-05 00:57:28 +0100 received badge ● Notable Question (source) 2013-11-11 15:48:11 +0100 received badge ● Popular Question (source) 2013-10-29 05:13:44 +0100 received badge ● Popular Question (source) 2012-10-11 16:29:13 +0100 received badge ● Nice Question (source) 2012-05-10 08:21:54 +0100 received badge ● Student (source) 2012-05-04 13:13:12 +0100 answered a question check if the result is a real number again, this works perfect :) for a in maxSol: if a[x] in RR: print RealField(50)(a[x])  2012-05-04 13:12:16 +0100 commented answer check if the result is a real number for self reference, this is what I got: 2012-05-04 13:08:14 +0100 marked best answer check if the result is a real number I think "a in RR" is what you want to use. Your first attempt could work too, using a try/except block. For testing integrality, or rationality, "in ZZ" and "in QQ" work similarly. And if you know the numbers you're checking are complex, you could also test to see whether their imaginary parts are zero. 2012-05-04 13:05:48 +0100 commented answer check if the result is a real number Thanks so much :) 2012-05-04 12:39:24 +0100 asked a question check if the result is a real number I get several results and want to check, which one is a real number. From trial and error, I can see that maxSol[2][x] is the only plausable solution. Is there something like isReal()? my attempt (don't laugh) ;) for i in maxSol: print RealField(50)(i) where I obviously get: TypeError: Unable to convert x (='..... 2012-03-01 10:08:52 +0100 commented answer solving sqrt(-1) to a real number that works perfect, thanks :) 2012-03-01 10:08:34 +0100 marked best answer solving sqrt(-1) to a real number sage: A(x)=x/2+(4-x*x)^(1/2) sage: solve(diff(A(x),x),x,to_poly_solve=true) [x == 2/5*sqrt(5)] 2012-03-01 10:08:34 +0100 received badge ● Scholar (source) 2012-03-01 10:08:29 +0100 received badge ● Supporter (source) 2012-03-01 09:26:06 +0100 asked a question solving sqrt(-1) to a real number Here is what I am trying to do: var('x') A(x)=x/2+(4-x*x)^(1/2) assume(0