MathGroup Archive 2001

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  • To: mathgroup at
  • Subject: [mg29380] roots
  • From: maarten.vanderburgt at
  • Date: Sat, 16 Jun 2001 02:47:52 -0400 (EDT)
  • Sender: owner-wri-mathgroup at


What is the easiest solution to finding the 13 (real) roots of 0.05 x +
Cos[x] == 0.
I can be easily seen that there are 13 roots by plotting:
Plot[{0.05 x,-Cos[x]},{x,-30,30}]
but this is not sufficient for finding accurate numerical values.

FindRoot only gives one value and it is hard to predict which root it will find with a specified start value:

In[83]:= FindRoot[0.05 x  +Cos[x] == 0,{x,0}]

Out[83]= {x -> -4.96317}

There are three roots closer to 0 then x == -4.96317

An NSolve only works for polynomials.

Is there no simple way to find all roots of such an equation, eventually within a specified range.

thanks for your help

Maarten van der Burgt

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