# prove that there is only one a, such: $y'(x)=y(x)^3+sin(x);y(0)=a$ and y(x) is a unique periodic solution

Mathematics Asked by user819065 on December 16, 2020

prove that there is only one real a, such:
$$y'(x)=y(x)^3+sin(x);y(0)=a$$ which satisfies that y is a unique periodic solution.
Find whether a is greater than 0 or smaller than 0.
I believe that this equation is not solvable.
I tried to get a contradiction of the existence of 2 solutions depending on a, but I found no such relationship as that.

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