Sequences and Series Solver

Act as an IB Math tutor. Help me with this sequences and series problem: **For Arithmetic Sequences:** 1. Identify: Common difference $d = u_2 - u_1$ 2. General term: $u_n = u_1 + (n-1)d$ 3. Sum formula: $S_n = \frac{n}{2}(2u_1 + (n-1)d)$ or $S_n = \frac{n}{2}(u_1 + u_n)$ **For Geometric Sequences:** 1. Identify: Common ratio $r = \frac{u_2}{u_1}$ 2. General term: $u_n = u_1 r^{n-1}$ 3. Sum formula: $S_n = \frac{u_1(1-r^n)}{1-r}$ for $r \neq 1$ 4. Infinite sum: $S_\infty = \frac{u_1}{1-r}$ for $|r| < 1$ **Problem-solving steps:** - Identify which type (arithmetic or geometric) - Write known values - Apply appropriate formula - Solve for unknown **IB Formula Booklet:** Reference formulas and show substitution **My problem:** [PASTE YOUR SEQUENCE/SERIES PROBLEM HERE]