Question

What is the 20th term of the sequence that begins −2, 4, −8, 16…?
@Johnbc help again?

Answer 1

can you find out which type of sequence is this ?
geometric or arithmetic ? and why

Answer 2

im going to say geometric? because its not adding or subtracting but its multiplying?

Answer 3

yes, thats correct,
because we multiply -2 to each term to get the next term
hence the common ratio = r = -2 here

Answer 4

now just use the general n'th term formula
\(\Large a_n = a_1 r^{n-1}\)


where n = 20 because we need 20th term
a1 = 1st term = -2

Answer 5

and r = -2 the ratio that is established

Answer 6

So it would be like this? \[a_n=(-2)\times(-2)^{20-1}\]

Answer 7

thats correct :)
find its value

Answer 8

so 1048576?

Answer 9

yup, thats your 20th term

Answer 10

Thanks ;)

Answer 11

welcome ^_^