Find a, for the following arithmetic sequence. S12=120, a12 = 21 a1 %3D

College Algebra
10th Edition
ISBN:9781337282291
Author:Ron Larson
Publisher:Ron Larson
Chapter8: Sequences, Series,and Probability
Section8.3: Geometric Sequences And Series
Problem 1ECP: Write the first four terms of the geometric sequence whose nth term is 6(2)n. Then find the common...
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**Problem Statement:**

Find \( a_1 \) for the following arithmetic sequence.

Given:
- The sum of the first 12 terms, \( S_{12} = 120 \)
- The 12th term, \( a_{12} = 21 \)

**Objective:**

Calculate the first term of the sequence, \( a_1 \).

**Instructions:**

Use the formula for the sum of an arithmetic sequence:

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

Where:
- \( S_n \) is the sum of the first \( n \) terms
- \( a_1 \) is the first term
- \( a_n \) is the \( n \)th term
- \( n \) is the number of terms

Substitute the known values to solve for \( a_1 \).
Transcribed Image Text:**Problem Statement:** Find \( a_1 \) for the following arithmetic sequence. Given: - The sum of the first 12 terms, \( S_{12} = 120 \) - The 12th term, \( a_{12} = 21 \) **Objective:** Calculate the first term of the sequence, \( a_1 \). **Instructions:** Use the formula for the sum of an arithmetic sequence: \[ S_n = \frac{n}{2} (a_1 + a_n) \] Where: - \( S_n \) is the sum of the first \( n \) terms - \( a_1 \) is the first term - \( a_n \) is the \( n \)th term - \( n \) is the number of terms Substitute the known values to solve for \( a_1 \).
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