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1. What is the explicit rule for the geometric sequence? 120, 40, 40/3, 40/9, 40/27, ...

2. What is the recursive rule for the geometric sequence? 10, −80, 640, −5120, ...

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Thank you to anyone who helps!

 Mar 13, 2018
 #1
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+2

The first one is:

Multiply each term by 1/3, so you have:

120, [120x1/3] =40, [40x1/3]=40/3, [40/3x1/3]=40/9...........and so on.

 

The second one is:

Multiply each term by -8, so you have:

10, [-8x10]=-80, [-80x-8]=640, [640x-8] =-5120........and so on.

 Mar 13, 2018
 #2
avatar+17330 
+2

The EXPLICIT formula for the first one:

 

r = 1/3    a1 = 120

 

an = a1 * 1/3^(n-1)

 

The RECURSIVE formula for the second one is

 

r = -8  

 

an = a(n-1) * (-8) 

 Mar 13, 2018
edited by Guest  Mar 13, 2018

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