+0  
 
0
244
3
avatar+117 

What is the first term of the geometric sequence presented in the table below?
 

n49

an−35185,293



Hint: an = a1(r)n − 1, where a1 is the first term and r is the common ratio.

 a1 = 13

 a1 = 3

a1= -1/3

 a1 = −13

 

Not D

failurewithasmile  Apr 14, 2017
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3+0 Answers

 #1
avatar+117 
0

n       4                9

an     −351         85,293

 

Hopefully that makes more sense of a chart lol.....

failurewithasmile  Apr 14, 2017
edited by failurewithasmile  Apr 14, 2017
 #2
avatar+117 
+1

@CPhill could you help me on this one as well?

failurewithasmile  Apr 14, 2017
 #3
avatar+75362 
+2

We have that

 

-351  =  a1 (r)^(4 - 1)

-351  = a1 (r)^3           divide both sides by r^(3)

-351/  r^3   =  a1         (1)

 

And

85293  = a1 (r)^(9 -1)

85293  = a1 (r)^8             sub (1)  into this

85293 = [ -351/r^3] r^8     

85293 = -351 r^5             divide both sides by -351

-243  = r^5                     take the 5th root of both sides

(-243)^(1/5)  = r  =  - 3

 

 

Using (1)

-351 / (-3)^3   = -351 / -27 =  a1  = 13

 

 

 

cool cool cool

CPhill  Apr 15, 2017

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