# Chapter 8, Sequences and Series - Section 8.2 - Arithmetic Sequences - 8.2 Exercises: 77

#### Work Step by Step

We are given the sequence: $1,2,3,4,5,... 12$ The sum would be: $1+2+3+4+...+12$ This is an arithmetic sequence with $a_1=1$ and $a_{12}=12$. Thus the sum is: $S_{12}=\frac{12}{2}(1+12)=6*13=78$

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