Posted by Embraced on Wednesday, January 11, 2012 at 7:18pm.
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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