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#14 Help

 Mar 16, 2018
 #1
avatar+100439 
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14.

 

The first term is  3(1)  - 4  =   -1    and the last is  3(18) - 4  = 50

So....the sum is

 

[ -1 + 50 ] (18/2)  =  49 * 9   =  441 

 

 

15.  The first term is  3(1)  - 3  =   0     and the last is  3(10) - 3  =  27

So  the sum is  [ 0 + 27 ] * (10/ 2)  =  27 * 5   =  135

 

 

 

cool cool cool

 Mar 16, 2018

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