Hi If geometric sequence = a1 = 3 a7 = 2187 and r = 3 find S7 in this Qustion which formula we use I use this : Sn = a1(1-r^n ) / 1- r the answer was = - 39 please help me ..
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If r < 1 or r > 1 also we use same formula ???
Yes, that's true. If r= 1, then the sum is na.
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