Q. Find an explicit formula for the geometric sequence −9,−18,−36,−72,… Note: the first term should be c(1).c(n)=
Identify sequence type and first term: Identify the type of sequence and the first term.The sequence is −9,−18,−36,−72,…, which is a geometric sequence because each term is obtained by multiplying the previous term by a common ratio. The first term is c(1)=−9.
Determine common ratio: Determine the common ratio r of the sequence.To find the common ratio, divide the second term by the first term: r=−9−18=2.
Write explicit formula: Write the explicit formula for the geometric sequence.The explicit formula for a geometric sequence is c(n)=c(1)⋅r(n−1). Substitute c(1)=−9 and r=2 into the formula.c(n)=−9⋅2(n−1).
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