# Algebra 2

posted by Embraced

Find a1 for the arithmetic series with Sn = 77, an=30, and n-7

1. Steve

Just as in your other post,

Sn = n/2 (a1 + an)

Only this time we want a1

77 = 7/2 (a1 + 30)
154 = 7a1 + 210
-56 = 7a1
a1 = -8

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