isabellagstclai isabellagstclai
  • 02-05-2017
  • Mathematics
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please help! this is for algebra 2. im not sure that im doing it correctly. thank you!

please help this is for algebra 2 im not sure that im doing it correctly thank you class=

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Аноним Аноним
  • 02-05-2017
a)    an = a1 + (n-1)d

so Sn  = (n/2)[ a1 + ( a1 + (n-1)d)]
            = (n/2) [ 2a1 + (n-1)d ]
            =  na1  +  n(n-1) 
                            --------  d
                                2



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