Question

Geometric Series. 2+4+8...n/4+n/2+n.
I have never done one of these summations before.

Answer 1

use the formula
a(r^n-1)/r-1
where r is the common ratio
and a is the first term of the series

Answer 2

so, a(2^n-1)/2-1

Answer 3

2(2^n-1)/2-1

Answer 4

yes then substitute value of n

Answer 5

ok, but what is n?

Answer 6

it is the number of terms u are including in ur GP

Answer 7

I dont know how many terms there are.

Answer 8

but if u dont know how many terms are there then leave it in terms of n
and ur sum WILL depend on the value of n

Answer 9

that is quite logical

Answer 10

ok, if i simplify that equation I get -2^n

Answer 11

is that the answer?

Answer 12

well, its 2n-1,from the answer booklet.

Answer 13

2n-1 doesn't seem correct. The sum of first 2 terms (n=2) is 6. But, 2n-1 would give 3!! The correct answer is 2(2^n - 1). Another clue is that the sum increases exponentially, so there ought to be an exponential term in the answer!

Answer 14

you can test out your answer ex: 3rd term = n = 3, so 2n-1 would equal 5, which is wrong. 2(2^n-1) is the correct answer