Sn = a (r^n - 1)/(r-1)
so solve for a
The first term is never missing. If you have the sum of terms k+1 to n, then that is Sn - Sk and both of those include a.
How to find the First Term of a sequence in the Sum of the Terms of Finite Geometric Sequence?
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How to find a Sum of the Terms if the Fist Term is missing?
1 answer