Question

For the geometric sequence -8, 16, -32, find a5

Answer 1

For a geometric sequence the nth term a(n) = a(1)*r^(n-1). In this case we have
a(1) = 5 and r = -2, so a(n) = 5*(-2)^(n-1) and thus a(5) = 5*(-2)^(5-1) = 5*16 = 80.

Answer 2

find r
then \[a _{n}=a r ^{n-1}\]
where a is first term, r is common ratio.

Answer 3

does anyone know the answer to this

Answer 4

first we need to find the common ratio by dividing the 2nd term by the first term.
16/-8 = -2...and you will notice that every term, when multiplied by -2, gives you the next term.

now we will use this formula : an = a1 * r^(n - 1)
n = the term you want to find
a1 = first term = -8
now we sub
a5 = -8 * -2^(5 - 1)
a5 = -8 * -2^4
a5 = -8 * -16
a5 = 128

Answer 5

\[a _{5}=-8*\left( -2 \right)^{5-1}=-8\left( -2 \right)^4=-8*16=-128\]

Answer 6

oops...my bad....surjithayer is correct...because -2^4 is 16...not -16....sorry about that