Question

Find a formula for the general term an of the geometric sequence {−2,4,−8,16,…}.

Answer 1

apparently its not -2n

Answer 2

Is it multiple choice?

Answer 3

nope

Answer 4

Darn...hmmm....give me a sec k?

Answer 5

k

Answer 6

@Mertsj

Answer 7

Are you sure it's not -2n? That sounds right...it's the only thing I can think of.

Answer 8

thats what i tried first

Answer 9

now look at your series, what number has negative sign?

Answer 10

1st, 3rd, 5th, ....... it means your (-1) must has the exponent of odd number, right?

Answer 11

separate the (-1) to get the sign of numbers, you have, it should be (-1)^n

Answer 12

when n=1 ----> your first number has the sign -
when n=2 ---> your second number has the sign+
so on and so on
now, calculate the main number

Answer 13

1st number is 2
2nd number is 4 = 2^2 (pay attention into exponent and order of number, they are same)
3rd number is 8 = 2^3
4th number is 16 = 4^4
so on and so on.

Answer 14

combine sign part and main part
you have general form is (-1)^n 2^n

Answer 15

so the answer is (-1^n)(2^n)

Answer 16

pay attention in notation, it's (-1) ^n , not (-1^n) they are different

Answer 17

k thanks

Answer 18

yw