How do you use a graphing calculator to find the sum of the geometric series #Sigma 2(1/2)^(n-1)# from n=1 to 15? Precalculus Series Sums of Geometric Sequences 1 Answer Vinícius Ferraz Jun 5, 2017 #S_{15} =4* (1 - 1/2^15) = 3.99987792968750000000# Explanation: #a_0 = 2 ; q = 1/2# #a_{14} = 2/2^14 = 2^-13# #S_n = a_0 * frac{1 - q^n}{1-q} = a_0 + a_0 q + ... + a_0 q^{n-1}# #S_{15} = 2* frac{1 - 0.5^15}{1-0.5}# Answer link Related questions What is a sample problem about finding the sum of a geometric sequence? What is the formula for the sum of a geometric sequence? What is a sample problem about finding the sum of a geometric sequence? How do I find the sum of the geometric sequence #3/2#, #3/8#? What is the sum of the geometric sequence 3, 15, 75? What is the sum of the geometric sequence 8, 16, 32? How do I find the sum of the geometric series 8 + 4 + 2 + 1? How do you find the sum of the following infinite geometric series, if it exists. 2 + 1.5 +... How do you find the sum of the first 5 terms of the geometric series: 4+ 16 + 64…? How do you find S20 for the geometric series 4 + 12 + 36 + 108 + …? See all questions in Sums of Geometric Sequences Impact of this question 1727 views around the world You can reuse this answer Creative Commons License