 incorrect answer from solve() solving inequality - Printable Version +- HP Forums (https://www.hpmuseum.org/forum) +-- Forum: HP Calculators (and very old HP Computers) (/forum-3.html) +--- Forum: HP Prime (/forum-5.html) +--- Thread: incorrect answer from solve() solving inequality (/thread-13220.html) incorrect answer from solve() solving inequality - teerasak - 07-02-2019 08:21 AM I found the wrong answer when letting HP prime solving inequality: The calculator gave result where x<=0 which should not be the case as x is under square root, and it cannot be 0 as the denominator will be 0 The rest interval are correct. So the calculator needs to exclude x<=0 [attachment=7423] RE: incorrect answer from solve() solving inequality - teerasak - 07-02-2019 08:58 AM I see Wolfram alpha gives similar answer! [attachment=7424] RE: incorrect answer from solve() solving inequality - parisse - 07-02-2019 02:32 PM Even if x is negative, the expression 1/(x+sqrt(x))+1/(x-sqrt(x)) is real valued : normal(1/(x+sqrt(x))+1/(x-sqrt(x))) returns 2/(x-1) Therefore the Prime answer is correct, and x=0 is also valid (since the limit at x=0 is -2 and -2<=1). RE: incorrect answer from solve() solving inequality - teerasak - 07-02-2019 04:46 PM Thank you, parisse. For x is negative, it means that each of 1/(x+sqrt(x)), 1/(x-sqrt(x)) to be complex number. If so, that is correct. For x is zero, (1/(x+sqrt(x))+1/(x-sqrt(x))) = (x-sqrt(x) + x + sqrt(x))/(x^2-x) = (2x)/(x*(x-1)) and this will be equal to 2/(x-1) if x<> 0 (otherwise, it will be 0/0) So (1/(x+sqrt(x))+1/(x-sqrt(x))) when x=0 should be undefined. However, lim x->0 of (1/(x+sqrt(x))+1/(x-sqrt(x))) is -2.