## College Algebra 7th Edition

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: $S_{12}=\frac{12}{2}(1+12)=6*13=78$