Question

For my brother who's too lazy to get on.

Find the sum of a finite geometric sequence from n = 1 to n = 6, using the expression −2(5)n − 1.
1,223
−1,023
7,812
−7,812

Answer 1

take the expression −2(5)n − 1

plug in n = 1, n = 2, n = 3... until n = 6

then add up the results

Answer 2

So it would be -2(5)1 - 1? :O if I were to replace n with 1?

Answer 3

yes

Answer 4

I got -10

Answer 5

-2?

Answer 6

I got D. -7,812

Answer 7

if its a geometric sequence
shouldn't it be $$ -2(5)^{n-1}$$

Answer 8

Am I right @Vocaloid ?

Answer 9

oof morseo I think you're right

Answer 10

-2 * 5 = -10, -10 * 1 -10?

Answer 11

-2(5)^(1-1) = ?

Answer 12

Sorry :P

Answer 13

We want \[\sum_{n=1}^{6} -2(5)^{n-1} = -2(5)^{1-1} + -2(5)^{2-1} +-2(5)^{3-1}
\\ + -2(5)^{4-1} +-2(5)^{5-1} +-2(5)^{6-1}\]

Answer 14

Can you add those?

Answer 15

I'll have to wait till I get home.

Answer 16

It's D e.e