Question

Write the sum using summation notation, assuming the suggested pattern continues.

2 - 8 + 32 - 128 + ...

Answer 1

@ganeshie8

Answer 2

@SolomonZelman go ahead.. :)

Answer 3

the common ratio is ?
the number of term is?

now think of a pattern with "n" that will generate the sequence

Answer 4

(btw, I never liked starting with index 0)

Answer 5

So, it appears like you have ∞ as the number of terms (on top of the Σ) in every choice.
So you know what goes on top.

Answer 6

Then on the bottom index of n=0.

Answer 7

So, in which of the option will we get the 1st term of -2 when n=0, the 2nd term when n=1, the third term when n=2, and on ... ?

Answer 8

You can try writing the first terms just looking at each answer choice if you want to.

Answer 9

the second choice

Answer 10

No, because you start plugging like this

n=0 , 1st term
n=1 , 2nd term
n=2 , 3rd term


and not

n=1 , 1st term
n=2 , 2nd term
n=3 , 3rd term

Since you started with an index of 0.

Answer 11

index is the bottom of Σ

Answer 12

so it would be addition, so the first choice

Answer 13

I doubt that because you have 2, -8 AND THEN 32.
It is definitely multiplication.

Answer 14

when you took the firs attempt, you got the pattern right,


\(\normalsize\color{black}{ 2(-4)^{0}}\)

\(\normalsize\color{black}{ 2(-4)^{1}}\)

\(\normalsize\color{black}{ 2(-4)^{2}}\)

\(\normalsize\color{black}{ 2(-4)^{3}}\)


and on.

Answer 15

Which of the options generates that, (starting from n=0) ?

Answer 16

C

Answer 17

Yes, there you go !

Answer 18

yayyy

Answer 19

when you start from n=0 on the bottom of Σ, you start plugging in 0,1,2,3 and on for n.
When you have n=1 on the bottom, you start plugging in 1,2,3,4 ... and on
(same way, but you sart from whatever you have n equal to on the bottom of the Σ)

Makes sense ?

Answer 20

same way. but you start*