SOLUTION: Enter a recursive rule for the geometric sequence. −10, 20, −40, 80, … a(1)= a(n)=

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Question 1131037: Enter a recursive rule for the geometric sequence.
−10, 20, −40, 80, …
a(1)=
a(n)=
Answer by MathLover1(20850) About Me  (Show Source):
You can put this solution on YOUR website!

The formula for the general term for each geometric sequence is. Let's examine sequence A so that we can find a formula to express its nth term.
The fixed number, called the common ratio (r); so, the formula will be
a%5Bn%5D+=+a%5B1%5D%2Ar%5E%28n+-+1%29+
-10, 20, -40, 80, …
a%5B1%5D=+-10
r=20%2F-10=-2
a%5Bn%5D+=+-10%2A%28-2%29%5E%28n+-+1%29+

check the rule:
if n=4
a%5B4%5D+=+-10%2A%28-2%29%5E%284+-+1%29+
a%5B4%5D+=+-10%2A%28-2%29%5E3+
a%5B4%5D+=+-10%2A%28-8%29+
a%5B4%5D+=+80+-> true, given fourth term of the sequence is 80