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Find the first four terms of this geometric sequence A1= 3 and r=-3

User Victor Cui
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a(n)=-1(-3^n)

3, -9, 27, -81
User Cypherjac
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Answer: The first four terms of the given geometric sequence are 3, -9, 27 and -81.

Step-by-step explanation: We are given to find the first four terms of the geometric sequence, where

first term is 3 and common ratio is -3.

That is


a=3,~~~r=-3.

We know that

the n-th term of a geometric series with first term a and common ratio r is given by


a_n=ar^(n-1).

Therefore, the first four terms are


a_1=ar^(1-1)=3* (-3)^0=3,\\\\a_2=ar^(2-1)=3* (-3)^(1)=-9,\\\\a_3=ar^(3-1)=3* (-3)^2=27,\\\\a_4=ar^(4-1)=3* (-3)^3=-81.

Thus, the first four terms of the given geometric sequence are 3, -9, 27 and -81.

User Troyfolger
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