Question

The sum of an arithmetic series is 1356 and the first term is -1. If the common difference is 5, how many terms are in the sequence?

Answer 1

@katiebugg Sum of n terms is given 1356
First term \(a_1=-1\) and common difference=5
we know that sum to n terms is given as
\[S_n=\frac{n}{2}(a_1+a_n)\]
\(a_n\) is the last term
Do you get till this?

Answer 2

yess

Answer 3

we know \(a_n\) is given as
\[a_n=a_1+(n-1)d\]
d=common difference
n=no. of terms
so
sum will become
\[S_n=\frac n2 (a_1+a_1+(n-1)d)\]
now pluigin the numbers here and post what do you get, will you?