Question

What is the sum of a 7–term geometric series if the first term is –11, the last term is -171875 and the common ratio is -5

Answer 1

do you know the formula for Sum of terms of Geometric series?

Answer 2

also, for the n'th term of geometric series?

Answer 3

a1=-11 and a7=-171875

Answer 4

use these :
\(\Large a_n = a_1 r^{n-1}\)
\(\Large S_n = a_1 \dfrac{r^n-1}{r-1}\)