anonymous 3 years ago What is the sum of a 22-term arithmetic sequence where the first term is 56 and the last term is -28?

1. anonymous

$S _{n}=\frac{ n }{ 2 }[2a+(n-1)d]$

2. anonymous

or you can use $S _{n}=\frac{ n }{ 2 } (a _{1}+a _{n})$

3. anonymous

n=22, a1=56 and an=-28 put the values in, in the second formula and you will have the sum