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What is the first term in a geometric sequence if the common ratio is −2 and the sum of the first five terms is 77?
a1 = −7
a1 = 3
a1 = 7
a1= 1/7

Respuesta :

jongdae21
Answer is a1 = 7

Using equation (derived from formula to find sum of values in a geometric series),
[tex]77 \: = \frac{a(1 - ( { - 2}^{5}))}{1 - ( - 2)} [/tex]
Hence, solve for a.

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