A Problem about Limits of Sequence

I have been asked to solve the following problem:
Let $\set{x_n}_{n=1}^\infty$ be a real sequence defined by $$x_{n+1}=\frac{C}{2}+\frac{x_n^2}{2},$$  with $x_1=C/2$, where $C$ is a constant, try to show that

1. If $C>1$, then $\set{x_n}_{n=1}^\infty$ is divergent;
2. If $0< C\leq 1$, then $\set{x_n}_{n=1}^\infty$ is convergent;
3. If $-3\leq C < 0$, then $\set{x_n}_{n=1}^\infty$ is convergent;

Try to discuss the case of $C< -3$, is $\set{x_n}_{n=1}^\infty$ divergent?

If you have any idea, please tell me! Just leave a word below!

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