Hi,

$\displaystyle (\forall n \in \mathbb{N}) U_{n+1}=\sqrt{12+U_n} $ and $\displaystyle \ U_0=0$

I showed that $\displaystyle (\forall n \in \mathbb{N}) U_n<4$

But i don't know how to show that $\displaystyle 4-U_{n+1}\le \frac{1}{4}(4-U_n)$

Can you help me please????