How do you find A1 in a geometric sequence if A3=-8 and A6=1? Precalculus Sequences Geometric Sequences 1 Answer seph Nov 8, 2015 #A_1 = -32# Explanation: #A_n = A_1r^(n -1)# #A_3 = -8 = A_1r^(3-1)# #=> -8 = A1r^2# #A_6 = 1 = A_1r^(6-1)# #=> 1 = A_1r^5# #=> 1 = A_1r^2r^3# But #-8 = A1r^2# #=> 1 = -8r^3# #=> -1/8 = r^3# #=> r = -1/2# #A_3 = A_1r^(3-1)# #=> -8 = A_1*(-1/2)^2# #=> -8 = A_1*1/4# #=> -32 = A_1# Answer link Related questions What is meant by a geometric sequence? What are common mistakes students make with geometric sequences? How do I find the equation of a geometric sequence? How do I find the first term of a geometric sequence? How do I find the common ratio of a geometric sequence? How can I recognize a geometric sequence? How do I use a geometric series to prove that #0.999...=1#? What is the common ratio of the geometric sequence 7, 28, 112,...? What is the common ratio of the geometric sequence 1, 4, 16, 64,...? What is the common ratio of the geometric sequence 2, 6, 18, 54,...? See all questions in Geometric Sequences Impact of this question 7017 views around the world You can reuse this answer Creative Commons License