Please help! this is for algebra 2. im not sure that im doing it correctly. thank you!

asked Sep 4, 2018 36.5k views

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5 votes

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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