Sum of the First 10 Terms of the Sequence Defined by \( a_n = 3n + 2 \)

Understanding arithmetic sequences is fundamental in mathematics, especially when calculating cumulative sums efficiently. One such sequence is defined by the formula \( a_n = 3n + 2 \), where every term increases consistently. In this article, we explore how to find the sum of the first 10 terms of this sequence using a step-by-step approach grounded in mathematical principles.


Understanding the Context

Understanding the Sequence

The sequence is defined by the closed-form expression:

\[
a_n = 3n + 2
\]

This linear expression describes an arithmetic sequence, where each term increases by a constant difference. Let’s compute the first few terms to observe the pattern:

Key Insights

  • \( a_1 = 3(1) + 2 = 5 \)
    - \( a_2 = 3(2) + 2 = 8 \)
    - \( a_3 = 3(3) + 2 = 11 \)
    - \( a_4 = 3(4) + 2 = 14 \)
    - ...

From this, we see that the sequence begins: 5, 8, 11, 14, ..., increasing by 3 each time.


Identifying the First Term and Common Difference

From \( a_n = 3n + 2 \):

Final Thoughts

  • First term (\( a_1 \)):
    \[
    a_1 = 3(1) + 2 = 5
    \]
    - Common difference (\( d \)): The coefficient of \( n \) — here \( d = 3 \).

Since this is an arithmetic sequence, the sum of the first \( n \) terms is given by the formula:

\[
S_n = \frac{n}{2}(a_1 + a_n)
\]

where \( a_n \) is the \( n \)-th term.


Step 1: Compute the 10th Term (\( a_{10} \))

Using the formula:

\[
a_{10} = 3(10) + 2 = 30 + 2 = 32
\]


Step 2: Calculate the Sum of the First 10 Terms (\( S_{10} \))