Question

Find the sum of a finite geometric sequence from n = 1 to n = 6, using the expression −2(5)n − 1

Answer 1

@hwyl can you help?

Answer 2

\[\sum_{n=1}^6-2(5)^{n-1}\]?

Answer 3

i mean is that the question?

Answer 4

i think so.. i don't remember how to do this

Answer 5

pull the minus two out first, deal with it at the end

Answer 6

\[\sum_{n=1}^6-2(5)^{n-1}=-2\sum_{n=1}^6(5)^{n-1}\]

Answer 7

then \[\sum_{n=1}^6(5)^{n-1}=\frac{5^6-1}{5-1}\] compute that, multiply the restult by \(-2\)