The exercise is about a recursive sequence $(u_n)$, with the first term $u_0 = 1$, and the recursive relation given by:
$u_{n+1} = \frac{u_n}{3 - 4u_n}.$

The questions in the exercise are:

1. Question 1: Show that the sequence $(u_n)$ is well-defined and $u_n < 0$ for all $n \in \mathbb{N}$.

2. Question 2: Based on this, deduce whether the sequence $(u_n)$ is increasing or decreasing and justify.

3. Question 3: (a) Define a new sequence $v_n$ such that $v_n = \frac{-1}{u_n}$.
   (b) Prove that $(v_n)$ is a geometric sequence, and find its common ratio $q$ and initial value $v_0$.

4. Question 4: (a) Express $u_n$ in terms of $n$.
   (b) Deduce whether the sequence $(u_n)$ converges, and if so, find its limit.

Would you like me to start solving these step by step or focus on a specific question?