What is Sn for the arithmetic series with d = -4, an = 27, and n = 9? Precalculus Sequences Arithmetic Sequences 1 Answer Trevor Ryan. Jan 30, 2016 #99# Explanation: We may use the formula for the sum to #n# terms of an arithmetic series : #sum_(k=1)^n[a+(k-1)d]=n/2[2a+(n-1)d]# #=9/2[(2)(27)+(9-1)(-4)]# #=99# Answer link Related questions What is a descending arithmetic sequence? What is an arithmetic sequence? How do I find the first term of an arithmetic sequence? How do I find the indicated term of an arithmetic sequence? How do I find the #n#th term of an arithmetic sequence? What is an example of an arithmetic sequence? How do I find the common difference of an arithmetic sequence? How do I find the common difference of the arithmetic sequence 2, 5, 8, 11,...? How do I find the common difference of the arithmetic sequence 5, 9, 13, 17,...? What is the common difference of the arithmetic sequence 5, 4.5, 4, 3.5,...? See all questions in Arithmetic Sequences Impact of this question 2238 views around the world You can reuse this answer Creative Commons License