1. We are given a recurrence relation $u_{n} = 3u_{n-1} - 1$ with initial term $u_1 = -1$. We want to find the general term $u_n$.
2. The recurrence is linear and non-homogeneous. First, solve the associated homogeneous recurrence $u_n^h = 3u_{n-1}^h$.
3. The characteristic equation is $r = 3$, so the homogeneous solution is $u_n^h = A \cdot 3^{n-1}$ where $A$ is a constant.
4. Next, find a particular solution $u_n^p$ to the non-homogeneous recurrence. Since the non-homogeneous term is constant $-1$, try a constant solution $u_n^p = C$.
5. Substitute $u_n^p = C$ into the recurrence:
$$C = 3C - 1$$
6. Solve for $C$:
$$C - 3C = -1$$
$$\cancel{C} - 3\cancel{C} = -1$$
$$-2C = -1$$
$$C = \frac{1}{2}$$
7. The general solution is:
$$u_n = u_n^h + u_n^p = A \cdot 3^{n-1} + \frac{1}{2}$$
8. Use the initial condition $u_1 = -1$ to find $A$:
$$u_1 = A \cdot 3^{0} + \frac{1}{2} = A + \frac{1}{2} = -1$$
9. Solve for $A$:
$$A = -1 - \frac{1}{2} = -\frac{3}{2}$$
10. Therefore, the explicit formula for $u_n$ is:
$$u_n = -\frac{3}{2} \cdot 3^{n-1} + \frac{1}{2}$$
This formula allows you to compute any term $u_n$ of the sequence.
Recurrence Relation 2F406A
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