We use cookies to personalise content and advertisements and to analyse access to our website. Furthermore, our partners for online advertising receive pseudonymised information about your use of our website. cookie policy and privacy policy.
 
+0  
 
-1
196
3
avatar+4116 

Help 17,18

 May 17, 2018
 #1
avatar+101360 
+1

17

 

5th term  = 140

7th term = 35

 

We have that  

 

(140)r^2  = (35)       where r  is the common ratio

 

Divide both sides by  140

 

r^2  = 35/140  =  1/4        take both roots

 

r = +/-  sqrt  (1/4)   =  +/- 1/2

 

So....note that the 6th term could be  (140)(1/2)  = 70

Or.....the 6th term could be (140) (-1/2)  =  -70

Thus.....  ± 70   is correct

 

 

 

cool cool cool

 May 17, 2018
 #2
avatar+101360 
+1

18

 

Note that the  first term  is 2(1) + 1 =  3   and the last term  is 2(12) + 1  = 25

 

So...the sum is

 

[ first term + last term ]  *  [ number of terms ] / 2  =

 

[ 3 + 25 ] *  [ 12]  / 2  =

 

28 *  6  =

 

168

 

 

 

 

cool cool cool

 May 17, 2018
 #3
avatar
0

The Answer is 168.

.
 May 17, 2018
edited by Guest  May 17, 2018

14 Online Users

avatar
avatar