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julieefang
What is the sum of a 22-term arithmetic sequence where the first term is 56 and the last term is -28?
\[S _{n}=\frac{ n }{ 2 }[2a+(n-1)d]\]
or you can use \[S _{n}=\frac{ n }{ 2 } (a _{1}+a _{n})\]
n=22, a1=56 and an=-28 put the values in, in the second formula and you will have the sum