 another fsolve question - 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: another fsolve question (/thread-4194.html) another fsolve question - roadrunner - 06-20-2015 04:01 PM Can anyone tell me what I am doing wrong? I plotted the function ph2o(X) (code below) and touched Menu/Fcn/Tangent and, as expected, I saw the tangent line at the cursor location that I could trace up and down the curve. [attachment=2185] However, when I plot function tdew(X,15) (code also below) and touch the tangent soft-key I get nothing. When I touch slope I get NaN. [attachment=2187] I get the same result with newton, newtonj, and bisection solver. Am I doing something wrong, or is the calculator not capable of that operation on that function? Thanks for reading, Paul Code: ``` EXPORT ph2o(temp) BEGIN  local a,b;  b:=(temp+273.15)/273.16;  a:=1-1/b;  return 10^(10.79574*a-5.028*log(b,10)+   1.50475ᴇ−4*(1-10^(−8.2969*(b-1)))+   4.2873ᴇ−4*(10^(4.76955*a)-1)-0.2138602); END; export tdew(r,tamb) begin  LOCAL y,z;  r:=ph2o(tamb)*r/100;  z:="fsolve(ph2o(x)="+STRING(r,2,12)+",x,−50 .. 100, newton_solver)";  y:=CAS(z);  RETURN y(1); END;```