Q. Find an explicit formula for the geometric sequence21,−4,32,−256,…Note: the first term should be a(1).a(n)=
Sequence Type: We have the sequence: (21),−4,32,−256,…Is the given sequence geometric or arithmetic?(21),−4,32,−256,…Here, each term is multiplied by a common ratio.The given sequence is geometric.
Determining a1 and r: Determine the values of a1 and r of the sequence.First term: a1=21Common ratio: r=21−4=−8
Expression for an: Determine an expression to describe an. Substitute 21 for a1 and −8 for r. an=a1r(n−1) an=(21)(−8)(n−1)
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