Question

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

@dan815

Answer 2

Sn = a1 * r^n - 1
--------
r - 1

Answer 3

here a1 = -2 , r = 5, n = 6

Answer 4

Sn = -2 * 5^6 - 1 = 15624
-------- ------- = -7812.5
5 - 1 4

Answer 5

Is that right?

Answer 6

-7812

Answer 7

Can you help me with this one:

Find the sum of a finite arithmetic sequence from n = 1 to n = 15, using the expression 2n + 5.

Answer 8

i'm assuming 2n + 5 is the formula for the nth term

so first term would be 2+ 5 = 7
and 15th term would be 2(15) + 5 = 35


Sn = (n/2) ( a + l)
here n = number of terms, a = first term and l = last ( 15th) term

Answer 9

I dont understand what to do