SOLUTION: -10, 20, -40, 80

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Question 923193: -10, 20, -40, 80
Answer by MathLover1(20850) About Me  (Show Source):
You can put this solution on YOUR website!
{ -10, 20, -40, 80......}
all given terms are divisible by 5:
-10=5%2A%28-2%29
20=5%2A4=5%2A%28-2%29%5E2
-40=5%2A8=5%2A%28-2%29%5E3
:
:
in general:
a%5Bn%5D+=+5%28-2%29%5En for n={ 1,2,....,a%5Bn%5D }

check:
a%5Bn%5D+=+5%28-2%29%5En for n=1

a%5B1%5D+=+5%28-2%29%5E1=5%28-2%29=-10

a%5Bn%5D+=+5%28-2%29%5En for n=2

a%5B2%5D+=+5%28-2%29%5E2=5%2A4=20

a%5Bn%5D+=+5%28-2%29%5En for n=3

a%5B3%5D+=+5%28-2%29%5E3=5%2A%28-8%29=-40

a%5Bn%5D+=+5%28-2%29%5En for n=4

a%5B4%5D+=+5%28-2%29%5E4=5%2A16=80