Question

Math each geometric sequence with the correct sum. a1 = 343, an = -1, r = -1/7

Answer 1

sn = (a1 - r^n) / 1 - r
a1 = 343
n = -1
r = -1/7

now lets sub
s-1 = (343 - (-1/7^-1)/1 - (-1/7)
s-1 = (343 + 1/7^-1)/ 1 + 1/7
s-1 = (343 + .1429^-1) / 7/7 + 1/7
s-1 = (343 + 7) / (8/7)
s-1 = 340/(8/7)
s-1 = 340 * 7/8
s-1 = 2380/8
s-1 = 297.50

you should probably get a second opinion on this