Dear Frank,
It works, but it solves the equation for x. What I wanted to do is to substitute the a for the Cos[ x ] and get the equation. So I would like to convert
eqn={Cos[2 x] == 0}
into
eqn2={a^2-1==0}
using the function Eliminate.
But I'm getting
In[3]:= eqn = {Cos[2 x] == 0, Cos[x] == a}
Out[3]= {Cos[2 x] == 0, Cos[x] == a}
In[5]:= eqn2 = Eliminate[eqn, x]
During evaluation of In[5]:= Eliminate::ifun: Inverse functions are being used by Eliminate, so some solutions may not be found; use Reduce for complete solution information. >>
Out[5]= 2 ArcCos[a] == \[Pi]/2
In[6]:= eqn2
Out[6]= 2 ArcCos[a] == \[Pi]/2
So I wonder how to get the output
a^2-1==0
instead of
2 ArcCos[a] == \[Pi]/2
Thanks!
