Question

Help!
Find s25 for the following arithmetic sequence -7,-2,3,8,...

Answer 1

You know how to apply the formula
\[\LARGE S_n=\frac{n}{2}[2a_1+(n-1)d]\]?

Answer 2

you gotta find d

Answer 3

and d is just -2-(-7)=5

Answer 4

n will be the number 25,
and \(a_1\) is the first term, -7
subsitute in and evaluate

Answer 5

s(25)=25/2(2(-7)+25-1)5?

Answer 6

s(25)=625?