How do I get all solutions of the equation cos(x)==cos(3x) using solve() from Symbolic Math Toolbox ?

I’ve tried the following code:

syms x
h(x)=cos(x)==cos(3*x);
[sol,par,cond]=solve(h,x,'returnconditions',true)

sol =
pi*k

par =
k

cond =
in(k, 'integer')

But I expected to obtain: k*pi/2.

Where am I wrong ? Thanks in advance.

Answer 1

[David Goodmanson]

Hi Angelo,

You didn't go wrong, it's missing half of the roots. But this works

h(x)=sin(x+pi/2)==sin(3*x+pi/2);

go figure.

[Angelo Cacini]

Hi David, many thanks for your reply. This is a good workaround. Regards