1. The problem is to find the second longest side of a triangle given certain conditions. 2. To find the second longest side, we first need to identify all sides and their lengths. 3. If the sides are labeled $a$, $b$, and $c$, and we know their lengths, we sort them in descending order. 4. The second longest side is the one that is the second largest in length. 5. For example, if $a=5$, $b=7$, and $c=10$, then sorted lengths are $10$, $7$, $5$. 6. The second longest side is $7$. 7. If the problem involves algebraic expressions, we compare the expressions or values to determine the order. 8. Always check if the triangle inequality holds: $a + b > c$, $a + c > b$, and $b + c > a$. 9. This ensures the sides can form a triangle. 10. The final answer is the length of the second longest side after sorting and verifying the triangle's validity.