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Determine the sum of the first 30th term in the arithmetic series 3.5 + 2.7+1.9+...

Guest Jun 1, 2017
 #1
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3.5   + 2.7  + 1.9.......

 

The common difference is  - .8

 

The 30th term, a30,  is given by  :

 

a30   =  3.5 - .8(29)   =  -19.7

 

And the sum  is given by

 

[a1 + a30] * n / 2           where  a1   =  3.5,   a30  =  -19.7    and n   = 30

 

[ 3.5 +   -19.7] * 30 / 2   =   -243

 

 

 

cool cool cool

CPhill  Jun 1, 2017

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