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

Question

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

hartnn · Answer

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

tester97 · Answer

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

hartnn · Answer

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

hartnn · Answer

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

anonymous · Answer

and r = -2  the ratio that is established

tester97 · Answer

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

hartnn · Answer

thats correct :) 
find its value

tester97 · Answer

so 1048576?

hartnn · Answer

yup, thats your 20th term

tester97 · Answer

Thanks ;)

hartnn · Answer

welcome ^_^