Question

What is the 20th term of the sequence that begins -4, 8, -16, 32...?

Answer 1

-2097152 is the 20th term

Explanation:

Write geometric sequence as an explicit formula

`-4,8,-16,32\rightarrow-4(-2)^0,-4(-2)^1,-4(-2)^2,4(-2)^3\\a_n=a_1r^(n-1)\rightarrow a_n=-4(-2)^(n-1)`

Find the n=20th term

`a_(20)=-4(-2)^(20-1)=-4(-2)^(19)=4(-524288)=-2097152`