## katiebugg 3 years ago 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?

1. ash2326

@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?

2. katiebugg

yess

3. ash2326

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?