Given an arithmetic sequence $\{a_n\}$, we are given that $a_1 = 2$ and $a_2 + a_3 = 13$. We are asked to find $S_6$, which is the sum of the first 6 terms of the sequence.

ArithmeticArithmetic SequencesSeriesSummation
2025/4/10

1. Problem Description

Given an arithmetic sequence {an}\{a_n\}, we are given that a1=2a_1 = 2 and a2+a3=13a_2 + a_3 = 13. We are asked to find S6S_6, which is the sum of the first 6 terms of the sequence.

2. Solution Steps

Since {an}\{a_n\} is an arithmetic sequence, we can write an=a1+(n1)da_n = a_1 + (n-1)d, where dd is the common difference.
We are given a1=2a_1 = 2.
We are also given a2+a3=13a_2 + a_3 = 13.
Expressing a2a_2 and a3a_3 in terms of a1a_1 and dd:
a2=a1+d=2+da_2 = a_1 + d = 2 + d
a3=a1+2d=2+2da_3 = a_1 + 2d = 2 + 2d
Therefore, a2+a3=(2+d)+(2+2d)=4+3d=13a_2 + a_3 = (2+d) + (2+2d) = 4 + 3d = 13.
Solving for dd:
3d=134=93d = 13 - 4 = 9
d=3d = 3
Now we know a1=2a_1 = 2 and d=3d = 3.
The sum of the first nn terms of an arithmetic sequence is given by:
Sn=n2[2a1+(n1)d]S_n = \frac{n}{2} [2a_1 + (n-1)d]
We want to find S6S_6, so we plug in n=6n=6, a1=2a_1=2, and d=3d=3:
S6=62[2(2)+(61)(3)]=3[4+5(3)]=3[4+15]=3(19)=57S_6 = \frac{6}{2} [2(2) + (6-1)(3)] = 3 [4 + 5(3)] = 3 [4 + 15] = 3(19) = 57

3. Final Answer

57

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