0

please can someone help me solve 

 (x*L)+B*tan(x*L)=0,

solve for x when B=10;L=0.1. The equation looks innocent but I need to find 1st 5 roots of equ.

Dr. belisarius
  • 115,881
  • 13
  • 203
  • 453
salwa shaik
  • 1
  • Welcome to Mathematica.SE! I hope you will become a regular contributor. To get started, 1) take the introductory [tour] now, 2) when you see good questions and answers, vote them up by clicking the gray triangles, because the credibility of the system is based on the reputation gained by users sharing their knowledge, 3) remember to accept the answer, if any, that solves your problem, by clicking the checkmark sign, and 4) give help too, by answering questions in your areas of expertise. – bbgodfrey Oct 07 '15 at 01:09
  • Plot the function to see where the roots are, then use FindRoot to obtain the numerical values. The first is, of course, at 0. The second is at 28.6277. – bbgodfrey Oct 07 '15 at 01:15

1 Answers1

1

If you constrain the domain of x you can use NSolve

B = 10;
L = 1/10;

eqn = (x*L) + B*Tan[x*L] == 0;

soln = NSolve[{eqn, 0 <= x <= 140}, x, Reals, WorkingPrecision -> 10]

(*  {{x -> 0}, {x -> 28.62772588}, {x -> 57.60557933}, {x -> 
   87.08313831}, {x -> 117.0267808}}  *)

Verifying roots

And @@ (eqn /. soln)

(*  True  *)
Bob Hanlon
  • 157,611
  • 7
  • 77
  • 198