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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