Question

What is the 19th term of the geometric sequence ? -2,4, -8 , 16 .... Can someone please help? thanks.

Answer 1

can you identify the common ratio... what each term is being multiplied by to get the next value

Answer 2

what do you mean ?

Answer 3

r=?

Answer 4

Oh it doesn't say :(

Answer 5

-2 x ? = 4

4 x ? = -8

-8 x ? = 16

whats the value of ?

Answer 6

R= -2 I think.

Answer 7

4 divide by -2, you're rite

Answer 8

it's -2

Answer 9

Ok so now what do I do ?

Answer 10

and a=-2 to right?

Answer 11

thats correct...

now the formula to use is

\[a_{n} = a \times r^{n - 1}\]

from the information a = -2 and n = 19, and you found r = -2 so substitute the, and calcuate the answer

Answer 12

ok thnk u :)

Answer 13

for you to get the right answer you'll need

\[a_{19} = -2 \times (-2)^{19 - 1}\]

Answer 14

-2(-2)^18

Answer 15

is the answer 990 for the 19th?

Answer 16

or no

Answer 17

try

\[a_{19} = -2 \times (-2)^{18}\]

Answer 18

k

Answer 19

ok that will be \[a19=-524288\] correct?

Answer 20

thats it

Answer 21

-524288

Answer 22

thanks so much