First of all: I'm so sorry, I posted my question to a wrong place ( into the poll).
So I copy here the question and the answer of jakubi and my reply to jakubi.
Question:
I would like to solve the following system
x*(2*sin(x)*y^2+x^3*cos(x)+x*cos(x)*y^2) = y*(2*sin(y)*x^2+y*cos(y)*x^2+y^3*cos(y)),
-x*sin(x) = y*sin(y);
Until I have founded only the solutions
x = k*Pi, y = +/- k*Pi; k is any integer.
jakubi's answer:
more solutions