Question

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

Answer 1

A(n)=-1(-3^n)

3, -9, 27, -81

Answer 2

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

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

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